Hi lock....There's units available but as far as clearance for the four speed I'm not sure.
I'm using a TH350C and have loads of room,relatively speaking.
Here's one from Pirate Jacks
It uses the smaller 7" booster for maximum clearance.
Not sure if this helps you,but maybe someone else who's done the conversion with a manual trans will chime in....

1950 Chevy Advance Design 3100 in Scotland
In the Stovebolt Gallery
More pix on Flickr.
I've definately got this truck thing in my blood ... my DNA sequence has torque settings
"Of all the small nations of this earth,perhaps only the ancient Greeks surpass the Scots in their contribution to mankind" Winston Churchill.