The bores on the 20 bolt and the 14 bolt 3.8 are too thin, and the 4.1 is no different. Thin walls flex, and that causes blowby, even if everything else is right, nothing will compensate for cylinder wall flex.
If you are dead serious, I'll tell you how to get blowby to a minimum. But a bunch of people are going to tell you I don't know what I'm talking about. It ain't gonna be easy, it ain't gonna be cheap, so if you want cheap and easy, just ignore this post.
First, toss all those trick rings in the trash. Why? Well Winston Cup teams can get any ring they want, and they use Speed Pro rings, with no tricks at all. A good set of Speed Pro File Fit single moly rings with medium tension oil rings will seal a cylinder as tight as anything you'll find. Forget static leakdown tests. Any "gapless" ring will look good there, but you don't build boost and make power sitting still with the engine off, do you? You want a dynamic blowby test under power. Winston Cup teams test that way, they don't "leak' an engine for any reason other than a baseline or a diagnostic test. By the way, call the Speed Pro Tech line, and ask them how to gap your rings. They'll tell you to gap the second ring WIDER than the top ring. DO IT that way, they didn't spend a couple hundred thousand dollars working with the best engine builders in the world for nothing. Take advantage of their work. The top ring seals only under pressure from the top, and any pressure between the top and second ring WILL UNSEAL the top ring. The second ring is intended to seal only when it is under slight crankcase pressure (ie. on the intake stroke, where there is normally negative pressure in a normally aspirated engine), it really only functions in a supercharged engine under part throttle as a compression ring that is used to pull a vacuum on the cylinder. Otherwise, it is just and oil scraper. That's all the second compression ring does under boost, scrape the rest of the oil off of the cylinder wall. Next time you get a set of rings (I mean good ones, not cheap "rebulder" sets) take a close look. On the top ring, you'll note a chamfer on the inside, and a dot or pip mark with instructions that the chamfer and the dot or pip faces the top of the piston. That is because compression pressurizes the ring from the top, via the clearance in the ring groove, to force it out to seal the cylinder. On the second ring, you'll notice the pip or dot is up, but the chamfer faces DOWN, and the ring is actually taped so that the BOTTOM edge is what contacts the cylinder. It is a reverse taper reverse torsion ring designed to seal under pressure from the bottom, and vacuum from the top, and any pressure from the top will unseat it. Rings only work under a pressure differential.
Next, pour the block up to the water pump holes with Hard Blok, and fill the lifter galley with titanium putty. Put an RJC girdle on the bottom, do all your oil system modifications, deburr your block, and have it machined. Start be having it align honed. Then, using a BHJ fixture called a Block Tru, have it paralell decked for height and squareness. Then chamfer and deburr the holes in the deck. You are now ready to install a set of ARP studs. Chase the bolt holes, get a set of flat heads, a set of gaskets identical to those you plan to use, a torque wrench, a bottle of Loctite primer, and a bottle of 271 RED Loctite stud and bearing mount. Use the primer to clean and prime each hole, then use the red Loctite on each stud, tighten it to the proper depth, finger tight only, and quickly install a gasket and head, then torque the head to 25 foot pounds. After the studs, the Hard Blok, and the titanium putty have cured for at least 48 hours, you are ready to take the heads off, keep the gaskets. Torque the mains, girdle and all, then bore the block. Then have the block cleaned and scrubbed to remove all boring residue from the cylinders. Measure each piston individually, and assign it a cylinder. Now, install a head gasket (you did save them like I told you, didn't you?) and a deck plate on each side, and torque them to the final torque ARP suggests. Then follow the Sunnen and Speed Pro suggestions for finsh, with a good set of fresh cleaned and dressed stones, flooding the cylinders with all the hone oil the machine will pump, and cleaning them often. Get a slick finish so the rings will seat without excessive heat and wear. Approach the final clearance size carefully, and avoid loading the stones or burnishing the bores. Yes, cylinders can be finished to +/- .0001, just like rod and main bores.
Now, here's the last part of the machine work. And there will be a lot of people who'll say don't do it. It won't work well on a car used more than a couple thousand miles a year on the street, but it won't hurt it either. Gas port the pistons. It DOES make a big difference, and it WON'T cause excessive wear, unless you use a crappy ring, or have a soft block. It will not be as effective on a 5000 RPM engine as it will on a 6000 RPM or higher engine, but it will make a difference. The reason is that it will compensate for any crankcase pressure by pressurizing the top ring from the top.
One other thing. If you take the trouble to mount an air pump (smog pump) to use to create negative pressure on the crankcase, it WILL seal the engine much tighter.
Of course, you can ignore all of that, and just decide that turbo engines are doomed to have blowby, leakage, and crankcase pressure. After all, it is your car, your money, and your engine.
Oh, by the way, when you pour the block, you'll need a dedicated stand alone oil cooler, at least a four pass unit. Put the RJC adapter for the big filter on it too.