A couple of questions for you to think about while making your decision:
-How important is originality vs. performance?
(i.e are you more likely to show or race your car).
-How good are your mechanical skills?
(i.e. can you do the work yourself or will it be farmed out)
-How much money do you have available for the project?
(related to the previous question)
And here are some options in rough order of expense and difficulty:
1. Hot rod your current 2.3L engine
2. Transplant a Turbo 2.3L EFI engine
3. Transplant a 302 or 5.0L 4bbl engine
4. Transplant a 5.0L EFI engine
Your 1974 has an additional issue in that the radiator support is too close to the location of a 302 engine to get a radiator in the usual place, requiring either placing the radiator on the outside of the support or changing the support to the '75-'78 type. This makes options 2. and 3. a lot closer than they would be for the later MII's. For the later MII's I would reverse these two options.
Another way to bypass the engine compartment issue would be to choose a more exotic (i.e. untried
) engine swap. The 3.0L or 4.0L V6 and 3.8L engines would fit without moving the radiator support. But all three pretty much require EFI.
The easiest way to do any engine swap is with a donor car present to remove parts from. The MII is a pretty easy car to swap engines in because all three factory engines used the same basic front-end parts, with only wiring, springs and the engine stands being different.
Let us know which option you would be interested in and we can discuss in more detail.