The 200 has a 67% overdrive. That would drop your 4.10 gears to about 2.75 in 4th. The 3.42's would be 2.29.

Also, the 200 should have lockup. If you run a higher stall converter, that would eliminate any slippage at cruise.

Downside is the 200R4 is going to be higher to rebuild and the converter is going to cost more. Since they ran 200's in GN Buicks, there is no doubt it will handle the power. IF it's built right. I can't give any info on what that will take.

I'm running a TH350 now, but when I get the chance I'm going to an overdrive trans.