I'm planning on an FMX to manual swap as well. I'm curious what 5 spd you're thinking won't hold up to the Cleveland. I would guess that the T5 would be too weak, but the Tremec TKO should surely be strong enough. Anyone chime in here? A toploader would certainly be cheaper, but overdrive would be nice to have.
I just did the conversion and spent $3000+. I was worried about P/N's though. Every thing including the shifter is 1970 correct. I'd say that it could be done for around $2500.
If it's a mild 351C a world class T-5 will hold up fine. I want a overdrive real bad now and wish that I'd considered a tremec. You should really consider a cable clutch 5 speed.