Looking to swap in an overdrive tranny, need advice & opinions

[cobra_4]

I've wore the search out today but I still can't really find the information I need so I'm just going to ask, even though I imagine it has been asked before. Some things have came up that calls for the need of a semi-daily driver with more than two doors so its time to steer my '89 2500 dually suburban more towards a daily driver. With 3.73 gears, no overdrive and a 454 under the hood gas mileage isn't its strong suit. 10-12 is about it.

So I'm thinking/wondering, if I go with an overdrive tranny, will it help the mileage? I'd like to go modern and do a 4l60e/4l80e, not sure what the advantages to either or are, or I could do a 700R4.

Any advice recommendations? Is there a drive shaft that will work or will I have to have one custom made? I assume the 4l's are longer correct? Any other issues I'm going to run into?

Also what about a shifter? Its on the column now, I'd love to retain that but I might could work a lokar floor shifter or something around my center console.