The AMC 150 and the 151 Iron Duke four cylinder are very different. The Iron Duke has the same bolt pattern as a Chevy small block V8. The AMC 150 has the same bolt pattern as a Chevy V6. The Iron Duke was put into all AMC cars, including CJs, until 1983. I have personally seen one 83 SX4 with the AMC 150, its wierd looking with that crazy engine shock. I believe the switch happened in the middle of the 83 model year, and I know that all 1980 to 1982 Eagles have the Iron Duke.
The AMC V8s and 258s used a different bellhousing but same input shaft. T5 and SR4 bellhousings are very cheap and common, you're not doing yourself a favor by retaining the Iron Duke chevy bellhousing. If you want more power the best option is to get a 6 cylinder cross member and a 4.0. The 4.0 is common and cheap, its rated at 195 HP, and it idles reliably. A Iron Duke gets about 80 HP, a 258 about 115, a stock 304 about 125 HP. You don't need to fabricate anything with a 4.0, its a bolt together solution with more power than you realistically need. Anything more powerful than that will also need a stronger transmission.
A chevy conversion in an AMC Eagle is a waste of time and money, besides being conceptually wrong. If you really want to make a custom engine mount, stick with the AMC V8s.
I personally restore 4 cylinder Eagles only. In PA that means I can legally use a universal catalytic converter without the input line on the side, and without all the pulseair clutter that goes with it. They are also the only Eagles that came with the awesome 3.54 gears that complement a T5 perfectly. All of them now have been switched over to 6 cylinders or V8s.
-Dave Spillane-