Well easy swap could be a 3.2/3.5 dohc engine from an isuzu, after that it's open to whatever you can either afford or have the skills to put in yourself. A fairly simple swap to me would be a chevy 4.3 V6. You could run EFI or Carb (up to you), if you go EFI you will need to get a computer/wiring to run it, also you would need an adapter froma Fiero store to adapt a GM 90* engine to the 60* trans, or you could run a chevy 2.8/3.1/3.4 and it will bolt up to the trans, just need to make motor mounts and what not for it. Your possibilities are endless!