Which Transmission for my 1966 C10 with 496 BBC

[Nils]

Hello,
I have a 66 C10 long bed with the original 283 sbc and the
3 on the tree manual transmission. Now i would put a 496 Stroker
Bbc with a automatic transmission in it. My Axle Gear Ratio is the original 3.73:1.
I am a cruser and not a racer. I would like to have low rpm on the highway.
I think about to put a TH400 in it. A 4L80E had an Overdrive, but i dont want to put much electric in the Truck. A Gear Vendor Overdrive is to expensive a think.
Maybe change a 3.08:1 Rear ?
Is there a other option?

Thank you all verry much.

Greetings from Germany.

Nils