IMHO, I wouldn't use an overdrive unless you're planning on driving it a LOT on the freeway..........as in at least 3,000 highway miles per year......

Since you already have the 727, why not run a 3.55 gear with a PTC 3,800 converter? With a 3,800 converter, you won't need the bandaid 4.10 gears anyway.........The car will still haul the mail and be freeway friendly...... If you decide that you still don't like that, sell the complete 727 with converter and switch over then.....

The car below has a 10.9 to 1, pump gas, stock stroke, 440 with RPM heads and runs 10.70's @ 124 with 3.55's and a small roller cam....... The car runs and drives great on pump gas, but we raced it on race gas just to make sure we didn't have any detonation issues.......

Here's some more info about it........