Is there a more cost effective way to adapt a c6 and a dana 20 than buying an advance adapter set up?
Not really.
Have you looked at using a ZF adaptor? It changes the face of the Dana 20 to look like that of a conventional full size transfer case. At which point you can attach it to the back of a 4WD version of the C6. Or just about any other transmission from the mid 70's to the mid 00's that runs the traditional 31 splines and big 6-bolt circle.
But no $50 junkyard solution exists.
If you are willing to change transfer cases, mix a bunch of parts around, and have about the worst possible low range ratio. You can use a small block C6 with a 70's long tailshaft and an NP205. That is the junkyard solution to using a C6 on the cheap. Don't forget to take off the suspension lift as you will run out of driveshaft angle to play with, but you can make it up with a body lift to clear the transmission better.
Is there a particular reason that you have chosen the C6??
Yep. I have one laying on my garage floor.... people are wanting crazy money for c4's these days.
Not really.
Have you looked at using a ZF adaptor? It changes the face of the Dana 20 to look like that of a conventional full size transfer case. At which point you can attach it to the back of a 4WD version of the C6. Or just about any other transmission from the mid 70's to the mid 00's that runs the traditional 31 splines and big 6-bolt circle..
I did a C6 in my last Bronco due to torque output of a stroker motor. Worried the little C4 wouldn't handle it. I don't think I would do it again. I started out with the advanced adapter kit and mated it to the 20. The AA output shaft broke within a few weeks. Probably torque related. I then went and found a big block C6 out of a 78 bronco with a 205 married to it. I had to have my small block C6 disassembled and I had the output shaft from the big block trans installed and then I mated it to the 205 and then built a custom cross member for installation. The biggest problem after all of that was the driveline angle. The new assembly was still long. It ate u joints and vibrated all of the time. I end up installing a TRU high9 high pinion rear end and that fixed it but it was a large investment. It was strong as hell, great for running the dunes and such but the low range was crappy.
It would be hard to beat a bolt in C4 even if there is some initial cost.
My 75 that John Dixon is building has a 351W/C6/D20. I got the C6/D20 in a deal and it was freshly rebuilt with the AA. So fresh he had to get it from the transmission shop then handed it to me. So that plus the value of the new AA and the D20 already mated to it made sense to use it in my build. I think it was exactly 4" longer but we pushed the rear axle back on this crawler so it fixed the rear driveshaft problem.
I always had it in my mind that the C4 couldn't stand up to the abuse that a C6 could but I've seen a lot of C4s in Broncos with high HP engines, or huge tires, or getting hammered on off-road. The NP205 is no doubt stronger but you lose the lower ratio like you have in the D20.
In a way I'm echoing what everyone is saying - there's pluses and minuses with both setups. With you being half way there since you have the rebuilt C6 already, it doesn't make the decision much easier lol.
Here's a couple John sent me. It's all I have right now.
Sell the c6. use money buy a c4 with adpt. all ready on it.