Fancyt, Carl's questions are spot on. You can go too high when making rear gear ratio changes if you have a .72/73 5th gear.
I have a .72 OD T5 with 31" tires (235/85/16) with 4.10 gears from a 67 Chevrolet C20 in my'51, 3600 with 216. It works fine as long as I'm running in flat country which is usually the case unless traveling. Well, got to add head winds to the list of when 4.10's are a bit too high. Of course all you have to do is drop down to 4th and all's well. With current gearing my truck will now run comfortably at 60-65 with a 75 mph max. But any hill or headwind and it more like 50/55 mph.
Fact is the original 4.57's were good with the .72 OD. Now if/when I get around to swapping in the 261 that's holding the floor down in a corner of the shop I think the 4.10's will be just right. And if I find a set of the hen's teeth 3.73's that were installed in a select few Eatons I'd be up to trying those. But no way with a 216 would I go with anything higher that 4.10s.
Good Luck,
RonR
