Would like to see if I can afford an aluminum driveshaft and radiator for my M body that is getting a 408 smallblock. I am sure nobody is making them for this application, so would have to be custom. Googling these parts brings up a lot of companies, so I'd like a few recommendations on quality, reliable sources. Parts gathering in progress during build. Thanks.

You can Google Action Machine in South Bend Indiana. I have them build driveshafts for me all the time and their prices usually match or beat anybody else. Not sure on the shipping.
For a radiator, the company selling them on here in the engine's for sale section can probably help you out. I had a customer buy one and put it in recently and it was a nice piece for the money.
Keith

Alright, thank you Keith. I appreciate pointing me in a direction and I will check out both.

champion for the alum radiator. Mine cools well with no leaks & only had to redrill 1 mounting hole on one side flange. A guy on here sells em. Most people seem to be happy with em & once in awhile a report of a twisted one so check for that ASAP if you get one & the occaisional mounting hole needing redrilled like I had to do but no big deal & I'm happy. For a perf app I think I'd get a 3 or 4 row core right off the bat. There was a thread on what to do to add a shroud but I missed it

I bought a dual pass one from four seconds flat.
pretty happy with it. at the time I wanted both inlet and outlet on the same side, but now it seems I need them on opposite sides and should get a 3 pass.

cross flow and no oil cooler but I run a seperate one anyway.

I went with Smiths Radiator. A little more expensive but looks similar to stock and all hand welded in the USA. I went with a 2 core but each tube is Inch and a quarter. Had to put in the Jag fan clutch and just had to shave off an eighth inch off the top of the shroud. everything else bolted up. Make sure you have the drive shaft balanced a couple times to recheck it and make sure your good on that.

I have an off-the-shelf aluminum shaft on my Supra, but they make custom shafts also. It's a nice piece, was a perfect fit, and it's been in there over 7 years on a DD.

http://www.driveshaftshop.com/driveshaft-measurement