GM was famous for making parts just different enough between models, engine sizes, and years, that parts did not interchange and you had to run to the dealer to buy the right stuff. The 350, on the other hand, stayed the same for many years. Thati s why I suspect the mounting points on the block are the same, and you just need the right engine mounts to match the cross member. My concern has to do with switching from a V-6 to a V-8. The rear of both engines should fall in the same place so the transfer case and mounts will be the same, and no changes are needed to the drive shafts. The new engine should only be longer in the front.
Along those lines, I do know that if this was a Dodge truck, the mounting points on the V-6 and the V-8 would indeed position both engines so the rears where in the same place. I suspect yours is the same. That means when they built the truck, it got a cross member as it came down the assembly line. It did not get one of multiple cross members based on the intended engine.
So, if the mounting points are the same on the 350's for both years, and the cross member is the same for both engine sizes, I would expect this to be a drop-in install with the engine mounts made for that engine size for that year truck. I would not be offended if you stop in at a GM dealership and verify this with an older mechanic. The people in the parts department can tell you if there is a difference in the frames between the two engines, and the mechanic should be able to tell you if the 350's from both years are the same.
If you look on the Rock Auto web site, you can look at pictures of the parts. The mount numbers are different between the two 1990's engines and a 1974 350, but I cannot tell if they will fit the same applications and were just redesigned. You might be able to spot a difference in number or location and spacing of the mounting holes.
Also, consider asking at some local salvage yards. They usually have a few people who have done all kinds of swaps at home and know what is different.
Saturday, April 22nd, 2017 AT 10:26 PM