Well, once again, I challenged the norm and everyone telling me that it could not be done. It can be done but BOY do I regret doing it. So much work (mostly because time consuming) figuring out the final configuration. The main and really the only reason I went ahead and did this is because I already had a early 90's 4.3 Vortec in excellent condition. The engine was from a 2wd 94 S10 and was going into a 4wd 97 Blazer

Here is the breakdown:
Parts from 94 S10 2wd engine: short block, water pump, harmonic balancer and flex plate

Parts from the 98 4wd Blazer engine: Cylinder heads, intake / injection system, exhaust manifolds (same as the s10's), All ignition components, oil pump and pickup tube (which I replaced anyway) front accessory drive set up (same as the S10)

Since the S10 was a 2wd I had to get a 4wd early 90's oil pan from the salvage yard since the bolt pattern for the oil pan is way different than the 98. The weak link in all of this is that you can not use the aluminum oil pan designed to bolt to the bottom of the transmission housing. Of course you could always do as Chevy has done for years and install support bars from the motor mounts to the bell housing. Of course all of that really isn't an issue if you did not plan on going off road and beating the crap out of your truck.

Regardless of what fit I would have replaced the following either way: intake manifold gasket, head gaskets, exhaust manifold gaskets, oil pump and pickup tube/screen and timing chain set. These are just good insurance while you have one of these engines out and they are such a pain in the butt to pull and install in the 4wd truck.

Either way, DON'T DO IT!!!!