Transmission dilemma

I have a 65 Dart GT convertible in decent shape. It is a slant 6 automatic with floor console.
The poor 6 is on its last legs with big time blow-by, low compression (90-100), and now the entire exhaust under the car got messed up when unloading it from a trailer.

I have a rebuilt 340 in my garage left over from a 73 Challenger, also I have a good 727 from the same car and a A833 OD with long tail, bell housing and shifter.
My dilemma is what direction to go - manual or automatic. (secret preference is the stick of course).
I am looking for a rear end - more than likely going to a 8 1/4 from a Cherokee, modified - it seems to be the most economical direction - either 3.55 or 3.07 based on the transmission.
Need a larger radiator, I have the a-body exhaust manifolds - will get a TTI DIY exhaust kit to go with it.
The front is 5x4.5 with disk brake conversion, the rear is 7 1/4 with small pattern but I have a spare 7 1/4 with large bolts, not yet installed.
I am doing all the work myself but since we are in a slump with this corona mess, the money is getting tighter(reduced weekly hours), so I am looking for the most economical option. Good thing is that I have more time to work on this project.
This is a cruiser not a racer, just having fun around town with it, and would like to get some hwy time too - not a screamer at 70mph.

What do you guys think is the most economical direction?

Thanks,

3.jpg

2.jpg

1.jpg