Engine choice

Picked up a decent roller 70 Challenger a few months ago.
It is a factory 318 auto, 2.74 gear. Motor and trans long gone.
I do not care about engine size matching vin number or trans matching fender tag.

What I have to at least get this car moving is the following:

A running 78 318 from one of my own vehicles, 84K miles, smokes some I would at least do a ring and bearing on it, and lap the valves in, minimum money spent, motor is already out of my old truck.

A 1970 340 still in a cuda' I bought, the boy I got the the car off, said his dad bought the car in 1991 drove it home and parked it, condition unknown but complete, and still in the car.
I knew his dad so true story.

A extra 340 but it has no main caps, or crank, so most expensive option, but would most defiantly be a good candidate for a 4" arm.

None of the above engines would stay in the Challenger, but would be a back up motor for my 340 4-speed Duster.
I have on back order a second gen hemi block, but who knows what decade Fiat will decide to start making old Mopar "P" number parts again.

Throw the trans in:

I have a 904 small block trans, decent shape already out, but I would freshen it up.

Or pull the 4-speed out of the cuda, it is complete down to the pistol grip, but every old mopar I own is a 4 speed.

Gears who knows, I have the following 8.75 gears complete, ready to bolt in:
3.23
4.30
5.38
and what ever is in the cuda' the way that car is optioned, with manual steering and brakes, and nothing but speed parts most likely between a 3.55 and 3.91.

The sad thing is this Challenger I bought just to just use extra parts up, but I keep buying more mopar stuff, dont really care about how fast it is, just how fun it is cruising.