The thm-350 behind a warm 454 isn't ideal, but neither is the 55-64 drop out style 8.2" rear axle assembly.
The traction device for this rearend are very expensive. The Eaton clutch type Posi is around $635. P/N EAT19686.
Even most ring and pinions are priced North of $300 brand new. Some ratios are almost $400 for the rng and pinion.
As stated by Pro StreetRob, these rear ends make it easy to chage ratios if you have 2 or more dropout center sections. One with an acceleration gear(low gear) and the other with a highway/cruising gear(higher gear ratio)
With the 454, low gearing really isn't needed for all around driveability as much as an engine that doesn't make as much torque, such as a 350.
I like this calculator as you enter in your stats and it gives you the cruise speed with a varying number of rear gear ratios.
MOTOR - A Rear Axle Calculator
3825rpm is need to cruise at 75mph with 4.10 gear, 27" tires, 1:1 3rd gear ratio.
3325 rpm is need for 75mph speed with 3.55 gears(this is a common gear for manual trans equipped cars of the era)
3200rpm is needed for 75mph cruising with 3.42's with the rest the same.
3150rpm is needed for 3.36 gears. This is a very common ratio as this is the gear that Powerglide equipped cars came with in the 1957 era. Ive got 3-4 center sections with varying gears in the garage.
The 1st gear final drive ratio with 4.10's and the thm-350's 1st gear of 2.52 gives you a 10.33:1 1sr gear final drive ratio.
With 3.36's that drops to 8.4:1.
In my 97 pickup I run the 700r4/4l60e with its 3.06:1 1st gear ratio and a set of 4.10's. That gives a 1st gear final drive ratio of 12.5:1 which is very short for street use. This setup requires 2675 to cruise at 75mph in Overdrive with the same 27" tires. I find this geared a bit to low for freeway driving at 75mph. A swap to 3.73's would bring my 75mph cruise speed down to 2550rpm.
It all depends on the intended use of the vehicle.
The good thing about the thm-350 (2.52 1st gear to 1.52 2nd gear)and even the 400(2.481st gear to 1.48:1 2nd gear) is that the rpm drop between the gears keeps the engine in the powerband better than the thm700r4/4l60e(3.061st gear to a 1.63:1 2nd gear). A higher stalling torque converter does help with this.
The newer 6 speed autos are even worse with their low 4.03 1st gear and 2.36:1 2nd gear. Larger rpm drop than even the 700r4/4l60e/65e/70e.
IMO the thm-200r4 is the best all around trans fpor gearing 2.74-1st gear 2.74 1.57 2nd gear 1:1 3rd and the high 0.67:1 OD ratio.(same OD ratio as 6th gear in the 6l80e trans).
A 4k85e with 200r4 gear ratios and weight loss would be the ideal trans IMO
peace
Hog