Any LowBuck but STRONG overdrive option?

if you swap in the A998/999 ratio box with a lock-up, the new low gear of 2.74 is 11.8% lower than the 2.45 of the 727. This would allow you to drop that same 11.8% out of the back.
Post #1 says you have 4.10s so, now yur down to 3.55s.
Ok 4.10 x 2.45=10.05, and 3.55 x 2.74=9.73; close enough..
Now for second gear; your current combo is
4.10 x 1.45=5.945, and with the other it would be
3.55 x 1.54=5.467, that's doable.
Your current combo with 27inch tires will do 65=3350 at zero-slip, possibly as high as 3500 at 4% but more likely, 3450 at 2.5% slip on flat level,hard ground.
The new combo will get you 65= 2900 in lock-up. that is a total reduction of about 16%.

The Mopar overdrive unit has a ratio of .69, which is a reduction of 1 minus .69=.31 or 31%; and that would bring your current [email protected]% slip, .. to
65=2311 in lock-up.

Will the A998/999 trans take 400hp?
With a few affordable mods, yes.
Except for requiring a longer driveshaft with a 904 yoke, a different flex-plate, and all the original KD mechanism, this is a bolt in.

credit to RRR for first mention in post #9