This question does NOT have an easy answer. But you insist? OK. heres what a LOT of people are running.
4 speed top loader with Jag IRS: 3.31 rear gear. 2800 rpm at 70 mph with 26.5" tires. 140+ top speed at around 6000 rpm.
Live axle (8.8 or 9") with 5 speed: 3.5 is pretty common.
Critical question: Are people HAPPY with these gear combos? A LOT of them are not! MOST folks wind up running whatever "rear gear" they got and whatever trans O.D. gear they got. Rarely do they consider their CAMSHAFT profile and THINK about the optimum "cruising rpm" and the CRITICAL 1st gear ratio.
5 speed with a 3.5 rear gear? Figure 25 to 30 mph TOP SPEED and tires going up in SMOKE in first gear. With a 460 you will quickly find 1st gear is not only "useless" it's downright dangerous! It will result in wheel spin when you LEAST expect it. Your 1/4 mile times will actually be FASTER using 2nd gear to launch (because 1st gear is a joke).
But with that high 5th gear O.D. (.68) your cruising rpm at 70 mph will be around 2000 (maybe less). Will your MOTOR like that ultra low rpm with that "radical" cam you got? Maybe not! You could drive faster! OR not use 5th at all?
HERE IS WHAT I WOULD DO:
I'd find me a 5 speed with a FIRST gear ratio between 2.32 and 2.78. 2.32 being a CLOSE ratio top loader gear and 2.78 being the WIDE ratio top loader gear. I'd find me a 5 speed with a .86 5th gear (just a little over drive, not NEAR as much as .68). Then I'd run a 3.31 rear gear. THEN I'd make sure my CAMSHAFT profile would "like" to cruise at about 2200-2300 rpm at 70 mph.
What you most likely WILL do:
Run the trans you got, wether it matches your camshaft profile or not. Pick a rear gear by looking at "top speed" and "cruising" rpm and pretty much ignore the 1st gear problem. Buy LOTS of tires looking for more "traction" and lots of "underwear" because the back end broke loose "again" when you least expected it!
,,,,choose wisely and good luck.
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