That TA kit isn't gaskets, they're plastic shims. I ordered a set a long time ago and relocated them to the trash can instead of even thinking about putting them on an engine.
It's hard to tell how good or bad your gasket surface is based on your pictures. I know how deceiving looks can be .vs real life with that stuff.
Personally if you're good enough to run a mill, you should be good enough to 'run' a surface plate. I'd start there.
The way I would do it is to first get a countersink and bevel all 6 threaded holes to spread out the load. Then make a few passes with something around 100 to 150 grit. Since lapping follows the hell out of the 80/20 rule, you'll be able to see what's going on pretty quickly. Then go from there. It's nice to have the entire thing nice and flat and square but that might not be in the cards. The part that REALLY need to be true and free of flaws is the section around the oil feel hole going to the engine. Leave a channel there and you've got a squinter (and not the good kind
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If you just have to absolutely positivity have to fire up the Bridgeport, you might end up going backwards. There's no reason to indicate of the gasket surface for your set up. You need to be PERFECTLY (as possible) square with your (worn) pump shaft bore. In an ideal world (ha ha) when that's trued in, you'll just happen to be square with the bottom of the gear pocket and the walls of the pocket will be indicated in at all axis.
If it takes a couple passes to get the feed and speed dialed in to leave a good finish, you might have just made your pump gears proprietary. from that point on. With a GM cover, the gears stick up above the gasket surface and the gasket make up the free play. The more chips you make, the more the gears will be out of the hole. The easy way is double up on the gaskets to keep from locking the pump up.... The correct way is to make the gears shorter.
I know for a fact you can get some beers and lap a thou or two off the gears, but I've never tried to machine therm. If you have a good set that might require a surface grinder to keep things right.... then some lapping.
If the gaskets surface has been lowered a lot, you'll want to fit the drive gear first, make sure it cleans on a fully torqued gasket that's had time to sit and take a set... THEN do the other gear and repeat the test with set time again.
There's a lot more to that surface than just a place to put a gasket and tighten some stuff down
After all that, you'll probably be good and fluid tight. The cover will still have the blemishes in the walls of the gear pocket but there's nothing that can be done for that short of serious heroics.
To answer your clearance questions, the best clearance is as tight as you can get it without having metal to metal. Thanks to thermal expansion of aluminum being right at double of iron, the clearances open up as the engine warms up.
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