Dellman, I'm not familiar with your year of truck, but most GM vehicles had a transmission crossmember that bolted to the frame. The transmission then mounted to the crossmember through a transmission mount, basically a metal plate with rubber bonded to it and a bolt hole on each side. This allowed the transmission a small amount of flexibility while supporting its weight and fixing it in position. I would check to see if the truck is supposed to have a crossmember supporting the transmission. Hanging a tranny off an engine with just the bellhousing bolts supporting it is a risk proposition.
If there is supposed to be a crossmember and yours is missing, I'd peg that as a major source of your center bearing travails. You can probably pick one up a the local junk yard for almost nothing and then buy a new transmission mount at your local parts store or online.
In fact, if there is supposed to be a transmission crossmember, if you go to a bigger, heavier driveshaft setup, you simply exacerbate the problem. I'd check that first, and fix it if it's missing, before even considering changing your setup.
Bad motor mounts are more likely to manifest themselves in excessive side to side movement when the motor is revved. I've seen broken mounts where the motor literally jumped up when it was revved (and the fan cut the radiator hoses even.)
rfs56trk, do you have some basis for the claim of poor design? I see this thrown out quite frequently when things aren't working right, but the cause of most problems is a lack of maintenance, missing or severely worn parts and/or a complete lack of understanding on the part of the person attempting to fix the problem.
For example, you will often hear, right here at Stovebolt, that Rochester Model B carbs are "awful", that they don't idle well, that they constantly leak, etc., etc. I have two on my truck. They don't leak, they idle fine and the truck runs like a scalded dog. They were rebuilt by a man who knows what he's doing.
The question I always ask is, would the manufacturer sell new vehicles that would fail early because of a poor choice of parts? Model B's were the standard carb for GM six cylinder engines for a number of years. Yes, modern carbs are better, but that's true of everything (in most cases.)
I doubt seriously that the driveline design of GM was poorly designed. I think it was probably state of the art for 1966.
