..... a bud down here found a 41 Plymouth and wants to make it a REAL cruiser .... better to start off with a later model combo ? .. with a 8 or 9 speed transmission ?

That would be really cool in my eyes. I like different. Seems you can get the 3.6 pullout cheap. I've seen a few low mileage less than $1000. If he was able to use the 8 or 9 speed fuel mileage and cruise speed would be very comfortable. Russell at sound German would be a good poc for transmission control. Keep us updated.

I would think a V8 would be the way to go. Look at the Plymouth Prowler a V8 would have that car a real serious
street rod. This is just my opinion. I know there is a lot of 6 banger guys out there. Again IMO

I think it sounds like a cool idea. If the 3.6 comes out of a Charger/300/Challenger, you're looking at 290-300hp in a car that's appreciably lighter than the donor.

There is a guy that swapped a Dart recently. I am not sure he is on here. I know he had his challenges but last I know it ran and drove. His was a manual transmission which added a degree of difficulty. I would think a swap retaining the automatic from a 300 or charger would be easier.

today's six cylinder cars can run rings around [most of] our old muscle, in stock form.
but with that said, "i coulda had a V8" seems to be a reasonable conclusion after a guy figures out the minute difference in both cost and transplant installation differences.
plus, as the older 5.7's are [somewhat] cheap these days, and will run great even with a ton of miles on them, the 8 gets my vote.
unless, of course, you already have the 3.6 and the necessary wiring to do the install.

Is there an aftermarket ECU that can drive the VVT and transmission? The factory one is probably so interconnected with other modules in the car a transplant would be next to impossible. Might be able to do it with a manual transmission....in the end a 5.7 is probably the easiest route as there is aftermarket support.

A good build thread on a guy who swapped one into an A-body on another forum

https://www.forabodiesonly.com/mopar/threads/72-dart-swinger-3-6l-pentastar-t5.361683/

umm, why????

I have a future build coming up, a 49 Dodge pickup. Its just sheetmetal and the original frame, that I'm not real excited to use that original frame. I have an option to use a pretty clean early Dakota 4x4 chassis, or I could build something from parts & pieces (I'm a retired welder).
For the most part, this truck will see very little work, pleasure driving mostly, and most of that will be in town or short highway trips.

Modern Mopar engine choices that can be found locally at reasonable prices are pretty limited. 3.6, 4.7 (which I will not use and are very hard to find good usable around here), or a 5.7. Then it goes back to the 5.9 or the 5.2, or even farther back, which barely falls under the "modern" engines.

I can live with a 100K engine that is in good shape, but 200K is a different story. In our area, the 5.7s are still bringing pretty big money, or have lots of miles on them. The 3.6 are pretty easy to find, and are pretty cheap. The 5.9 and the 5.2 are getting hard to find without huge miles on them. In town driving with any of the V8s get you 10-12 mpg, the 3.6 gets near 20 in town.

To put things in proper perspective, my 48 Plymouth coupe has a 3.9 with a 5 speed and I'm OK with that, the 3.6 actually has a lot more HP then the 3.9. With current gas prices hoovering around $3 a gallon and I don't expect them to go down much (especially since our state just added a 19 cents per gallon sales tax), I don't feel the need to feed, a Hemi to drive around town, and the Hemi power would probably get leadfooted me in trouble, the V6, probably not so much. Gene

Have you read about the difficulties and resulting expenses of dropping a 5.7 in an A body? That thing presents some hefty challenges to engine swap guys.

The 3.6 has good power, light weight, and smooth running. No, it won't go as fast as a proper V8 but it'll outrun lots of SBC swaps and be much nicer to drive.