Too high rpm - overdrive? Keisler?

Okay, I run a 73 Dart Sport.
318
Eddy RPM air gap
Eddy 1406 600 cfm carb
Comp Cam XE268H
Hooker competition headers with 2 1/2" exhaust
Stock (as far as I know) 904 column shift
2800 stall
Dana 60 w/ 4.10 gears
Mono leaf and Caltracs

As expected, with the new Dana the rpm's are extremely higher in all driving. My tach is broken until I install the new one on Monday, but I would guess that at 55 mph I am running near 3200 rpm and probably over 4000 rpm at 70 mph. I realized when I installed it that this would no longer be a highway car, but I need to get from point A to point B.

I have looked at aftermarket overdrive units that bring the final drive to around .87 and a Keisler manual conversion 5 speed that brings the final gear to .64. Any suggestions on the best way to go? One of these? Neither of them? I need ideas before my poor engine blows!