Joekatana would be a good option for sure.
I think with your transmission, you can swap to 12HT YES! H/2H (I wouldn't do this) and 2F, 3F (probably wouldn't do this either...I'd go V8 if I had to go that route) without changing transmission input shaft. Otherwise you are going to need to change at least the input shaft on transmission.
Then you are looking at a bit of fab for motor mounts, wiring (not much), fuel lines, cooling lines (possibly), throttle connection and all other bits and such.
The other, not so popular option, could be to swap to V8. I know I know, this is a Toyota site...but a used 12HT or 1HZ or 13BT is pretty pricey. A few 12HT/H55 combos were for sale from $5500 ~$7K on this forum. Ranging from 150,000Km to rebuilt within a few months.
You can pick up a nice low mile Chevy LS V8 for pretty cheap. You still have motormount, cooling, wiring transmission adapters to deal with...but you also have 300hp and parts you can basically find anywhere.
Just some options. At the amount of money I'm into rebuilding my 13BT, I could have done a V8 swap.