I can say that it can be done effectively if you put the time and effort into researching what you need. I can say this first hand as I have done this conversion and did 90% of it myself. Jono on the forums did the wiring for me.
Dont need custom engine mounts, other nissan mounts can be used which bolt to the u12 crossmember.
If you get a 50's series sr20 bellhousing (Easiest to source in NZ) then you use that with the gearset and outer casing from a u12 ka24e gearbox. I have been running it for 5+ years without the gears giving me any issues, that includes a day out on the track. The beauty of this setup is you keep the hydraulic clutch setup (using a gtir slave cylinder, I think) and you can use the stock ka driveshafts. If you can source an awd flywheel and starter motor you can run a skyline clutch (best thing I did to my conversion).
Ecu, Ive used a stock w10 avenir ecu (thats the engine I got) and put Nistune in it. Realtime tuning with the ease of using all your stock sensors etc.
Have a read through my project thread for a good run down of the conversion process.