The Olds rearend is an open 2.56. I could put a posi unit in it, change out the gears, rebuild it, then buy a brake kit for it. But, by the time I do that, I might as well just purchase a complete drop in.
I'd much rather get a nice 12 bolt for it, but boy they are spendy! I'm also moving away from my ultimate dream of a really massive big block, (750+HP) and realizing a nice 450ish HP Pontiac is likely in my future, so I'm considering saving the cash and compromising with the 10-bolt.
So you do not think that using the control arms too push the pinion into correct angle against the spring perches pushing the other way is a "bandaide" fix?
Thanks to all for any input!
Any rear end you purchase will be "spendy." The new Ford 9" cost me $2,800 to set-up/build the way I wanted and that is with 11" drum brakes. A new 12-bolt won't be cheap either. The Ford 9" in my opinion is the better choice because you can more easily swap out gearing by removing the center section complete. If you really wanted, you could have another center section/gears on hand and swap them out, ie local driving gearing versus long distance highway gearing. But, another investment for another center section. But still, easier to bring the center section to a local guy to have another gear set installed and set-up. A 12-bolt, you will have to drop the car off or bring the entire rear axle assembly to him.
Purchasing another 10-bolt and beefing it up to handle additional HP & TQ will be throwing good money onto bad. You seem to be on a budget, so why throw money away and have to repeat? I understand the "get by" thinking and have done it many, many times.
With 2.56 gearing, I take it is an automatic? 1966, if factory, is the 2-speed Super Turbine. Swapping out gearing is an option, but it appears you will most likely need a different carrier. I am no expert on the Olds rear, but I found this forum that can give you more info. I don't see rebuilding the rear axle assembly worth the higher expense required to do so and in the end, may not have a strong enough rear end: https://classicoldsmobile.com/forums...ear-end-87060/
The 8.5" from a 1971-72 Buick A-body can be built to handle the HP like any 12-bolt. Many racers use the 8.5" rear end, but you may find it hard to find an A-body 8.5" that'll bolt up. Check your local craigslist as they do pop up.
So, in my opinion, anyway you look at it, it will not be inexpensive to upgrade either the Olds 10-bolt or go with a new 12-bolt and add your accessories. The least inexpensive route might be to purchase a used 12-bolt with the gear ratio you want and then upgrade from there, but again, not going to be cheap
On the question of the upper control arms, I did not say the adjustables won't work. They should work. Your springs should not be forcing the rear-end in any direction. The springs should only sit on the spring perchs. The 1966 and 67 frames are the same, so the clamp plates or towers will work either way. If the springs appear to be angled in some way, you have other issues. There are different length control arms and perhaps wrong length control arms have been installed IF they are not the original ones. It is the lower and upper control arms that **** the pinion down/up. The Chevy websites say the lowers are all the same, but the uppers are not. In 1968 the frame is changed and the uppers control arms are shorter - the frames would be about the same as Pontiac A-bodies, as well as the Olds A-body. The 1964-67 are said to be 12 3/4" center hole to center hole at the bushing, and 10 1/4" on the 1968-72 upper control arms. So IF the 1970 Olds swap included the control arms, the upper arm length may be incorrect for your '66.
But, if bushings are worn out on the lowers, they can have an effect on the pinion angle and installing the adjustable uppers may not give you what you want if the lowers are shot and need replacement. But the adjustable upper arms can dial in the pinion angle.
And, nothing on a Pontiac is inexpensive and the bigger the HP/TQ, the deeper your pockets need to be.