Mike is absolutely right, in 96 Chevy made major changes to the 4.3, parts from 95 back are mostly different. I ran into EXACTLY this problem with a boat I once owned. It was a 95 Chris Craft that I bought with a blown 4.3 in it. I found a low milage 96 4.3 engine and rebuilt it to install. When time came to put the accessories on it almost none of it fit, like the intake manifold. So I had to buy brand new 96 parts to make it complete, and they were not cheap because my 95 had a carb on it and all the 96 up engines I could find in the junkyard were injected. So I had to buy a special marine intake that was something like $ 500.00. As I remember there were also differences in some of the ways things mounted.

The engine ended up costing me a whole lot more than I planned on but I was over a barrel as I had already spend a bunch of money rebuilding it. I think Mike is right that your cheap engine might end up like mine did.

Don