[G.M.]

Personal opinion, not expert. I have a number of 30's Fords with Columbia
rears. Your not going to see much difference between a GOOD running 21
engine and a later one for normal driving. I have some with 21 stud engines
and 24 stud engines. I like a 3:78 rear with the Columbia in all years. With a
Columbia it's like a 4th gear. Very seldom do you use Columbia in 2nd or 3rd,
at first it is experimental to play a little. You need to learn how to drive in
Columbia OD. At 65 no Columbia the engine is running pretty fast, in Columbia
at 65 it the engine sounds like it's going 45 MPH. You never start out in Columbia
and you plan ahead when coming to hills or small mountains, I get up to a faster
speed before getting into a large hill and very seldom have to drop out of OD. I
have all the controls installed so as soon as I press the clutch it drops out of OD
without pushing any switch. Non of mine are so called bullet proofed and never
had a problem in several hundred thousand miles in over 30 years. The only maintenance is squirting MMO in the inlet pipe of the shift cylinder once a year
to keep the leather cups soft. It's hard for me to drive an old Ford without a
Columbia. The Columbia is a 28 1/2% overdrive. G.M.