The Jeep engines were similar to GM engines, especially the inline 6's. Some of the others used Buick V6's, too. I don't know if the cam would fit the Fiero engines, but even if it would, I don't think I'd go there. In general, the Fiero 2.5 engine isn't of hop-up quality, without replacing most of the internals with some pretty expensive pieces. The 84 was the poorest of all. Cranks and rods just aren't that strong and the hp gain isn't worth the money. A 92 hp engine hopped up to 140 hp could be pretty expensive. Cheaper and easier done by just dropping in a good 2.8 Fiero engine or a 160 hp Camaro/Firebird 3.4.
Mercury Marine used the GM 4 cylinders in their stern drive systems throughout the 80's and 90's. The cam is different, in that it's designed to run at high rpm and under constant load. Using one of those engines and changing out the cam and the bolt-on stuff might give you a little better 4-banger.
I have a Yamaha-outfitted inboard that uses the GM 4.3. When I replaced the engine, the marine dealers wanted over 3,000 for a long block because it was a 'special marine engine'. I compared Yamaha and GM specs and found them to be the same, so I bought a rebuilt 4.3 for about $700. I just swapped in my marine cam, installed the engine and went skiing.
I just saw your post that you've got an 86. The engine was improved as far as the strength of the internals. It is a better engine than the 84. TopNotch is working on an 88, which was the better engine of all the Fiero 4's.
