I am curious, I plan a manual trans behind a tri-powered 300 in a 56 F100, I know I am going to have a hydraulic clutch set-up (under floor) and I was curious: which OVERDRIVE manual trans would be best?

I really do NOT want to use a mustang type T5.... would rather have a truck trans.. partly because I want to run a bench seat and a big tall retro rod style shifter.

long ago I had an 84 F150 2WD supercab longbed with a 300 and a 3+1OD manual trans, and it done everything I wanted it to, except beat Dad's 78 F100 with 240/3speed

 

If you're going with a hydraulic setup, I'd recommend either the ZF5 or the Mazda M5OD. The ZF5 is more expensive, but has a granny gear and is much more robust if you use your truck as a "truck".
The M5OD is a good every day "highway" transmission and is generally less expensive. Just be sure to double check its condition, and replace the rubber plugs near the top with brass ones, as the rubber ones dry, crack, drain fluid, and burn up the trans.

 

what years/models would I likely find the M5OD? I do not want a Granny gear

 

The M5OD came behind the 300 & 302 (will fit the 351, but those were pretty much all autos) from around 88 to 96. It was usually in F-150s since the F-250/350s received the ZF5.

M5OD:
1st: 3.90
2nd: 2.25
3rd: 1.46
4th: 1.00
5th: 0.80

 

that should work great with 3.55:1 rear gears and a 30 inch tall rear tire... (street radials on 20 inch rims)