18 spline A body 4 speed
If it's for street, and for a cam peaking at or near 5100, then
I highly recommend the 1x23, Commando gearset, in the which, the 3.09 low gear will allow a 16% lower gearset number, like 3.23s. The rest of the gears are the regular ratios.
But if you plan on running up near or into the 4 series rear gears, then I agree with
@Oldmanmopar in post 15.The splits are tighter, allowing the engine more time on the pipe., er cam, er the fat part of the powerband.
My engine, by it's trapspeed of 93 in the Eighth, looks to be making 430 hp, with a street tune. I installed my Commando in 2004 with a GVod behind it that I use as a Gear-splitter. I have not been able to break it, with 295/50s on the back, and I hold nothing back. But neither do I run a CFII disc.
Honestly, the 295/50s seem no quicker than the former 275/60s, but they are more predictable when drifting the turns, and recovery is nearly instantaneous by just slipping the clutch as may be required.
If you're concerned about breakage, just buy a spare box.
Prior to Covid, I used to buy A833ods for as low as $50, towards the end of swapmeets. You can't even buy a 4-pac of new brass for that now.