The 3800 Series II engine went into production in 1995, that year it was only offered as the naturally asperated version. Starting in 1996, all 3800's were Series II.
The Series II 3800 has a 1" shorter deck height compared to the Series I 3800 and 3.8L Buick V6. Furthermore, the Series II heads offer a symetrical port design which means earlier intake manifolds and cams would not work with them because of the even valve layout (IEIEIE). So even if you bolted a set of these heads on an earler 3800 or 3.8 (which I think you can), there is no production intake that would mate up to them. All 3800 (incl series II) engines had STANDARD FLOW cooling systems, just like the 3.8L. The Series II engines also had the following features:
-cross bolted powdered metal main bearing caps
-hydrualic roller cam
-roller rocker arms
-balance shaft
-crank driven oil pump mounted in timing cover
As for the 3800 Series I engines, here are the differences I know of:
88?-91 Vin C:
-hyd. roller cam
-balance shaft
-FWD bellhousing
91-95 Vin L:
-same as vin C but heads had a passage cast in them for internal PCV and crankcase vent provisions. This allowed these to be incorperated into the intake manifold without external lines.
Series I 3800 SC differences: According to my info, the crankshaft, heads, block, and pistons are the same part number between the Vin L N/A engine and Vin 1 SC engine. Only the connecting rods are different.
Series II 3800 SC differences: According to my info, the crank and block are the same p/n, but the rods and pistons are beefier. This would also mean the cranks are balanced differently. The cylinder heads are of the same casting number, however SC engines have injector bosses machined directly into the heads. The N/A heads have these bosses, but the holes are not machined.
From what I know of the 3.8L buick engine, you could use either 3800 vin C, vin L, or vin 1 heads on it along with the appropriate intake manifold. You can reverse the intake no problem. However, you must keep in mind the exhaust ports are different compared to 3.8L buick engines which means custom headers would need to be made.
If you want more info on the 3800 differences, check out my website using the URL in my sig.