Saturn was designed from the ground up so it does not share any standard gm anything. I need to find someone with a junk block so i can get the bolt pattern measurements off of the back of the block because i cannot find them anywhere on the internet.
Well, if you're sure... some Honda and Isuzu drivelines also used the Corporate V6 pattern, and some of the transverse V8s, so that's just plain weird.
If you make an adapter, the generally accepted maximum figure for axial misalignment of the crank to input shaft is .015".
Generally there are two dowels that locate the block and bellhousing. The rest of the bolt holes have clearance. You don't have to sweat the alignment of those.
Sometimes you have bolt holes that intersect, or line up with something they shouldn't. It doesn't hurt to twist the transmission and bellhousing off vertical if you need to. Chevy twisted the T-5 transmission of the previous-generation Camaro quite a bit (15 deg?) to move the shifter closer to the driver.
Not every bolt is absolutely necessary, if you wind up with a bad interference problem somewhere. Bottom bolts are more important than upper, since they bear the tension load from the weight of the engine and transmission across their mounts.
The 99% alignment method is to make a mandrel to bolt onto the back of the crank, which slides over the bearing retainer where the throwout bearing moves. Then you can slide the engine and trans together and work on your adapter.
The 100% method is to make a bar that bolts into the mains and extends into the input bearing recess of the transmission. Not worth the effort in my opinion.
Make sure the pressure plate swings inside the bellhousing without hitting anything, and there's room for the throwout bearing and actuator!
In some cases, if you slide the engine and crank together with an adapter as above, you can weld tabs onto the outside of the bellhousing, or weld tubes in, and avoid the whole "adapter plate" thing. Grind, fit, then have it all TIGged together. Or hee-hawed, or mamawed, or whatever they call it now.