4 Speed w/ Overdrive Any Good?

In that link above is the bellhousing I have under "OD A-833 Behind A Big-Block."
So with a 4.35 diameter retainer bellhousing they modified both the bellhousing and the retainer, but it appears the better solution would be to modify just the retainer.
I'll have to do some more research.
My shifter is an old school Hurst, where the chrome handle is actually part of the shifter, not bolted on. I've seen the stock OD shifters, I'm just not convinced I can use the one I have.

Stupid Question- can you put the overdrive gear on third in a regular 833?
It sounds like the OD goes 1st, 2nd, 3rd, 4th, then back to 3rd. Is 3rd gear the same gear each time, or is there a 3rd gear and an overdrive gear?
I obviously don't know what I am talking about, lol.