[Hybrid1990crx]

If you want to use a si or dx tranny, you will have to change axles si and dx are 26 splines. you'll also need si hubs. A dx tranny is basically a HF tranny but without a 5th gear, so you dont want that for performance. Spend the money for a Si tranny you'll thank yourself for not skimping out in the long run. you can use your stock mounts, but they might be a little beat after years and use, so new oem mounts will probably help, or get engery inserts a shop will press them in for fairly cheap. I'd also get a obd1 ecu and get a conversion harness to run it, but you could also do what turtle said and run a pm6 with a vafc, or if you are on a budget get a rpm activated switch.