I have a Chevy 10-bolt with an 8.5 inch ring gear from a '78 Nova. It's time to replace the gasket so I have been looking at aftermarket covers with a drain plug on the bottom to make future work less messy. I see several different covers for 10-bolt/8.5 at the usual places but the applications (if listed) vary. For instance, this JEGS unit ( https://www.jegs.com/i/JEGS/555/62553/10002/-1 ) is for a 10/8.5 but it doesn't list the '78 Nova. This cover ( https://www.jegs.com/i/JEGS/555/62573/10002/-1 ) looks more like mine and does list the '78 Nova but doesn't have the drain plug on the bottom. Other vendors don't even list the applications. Are all the 10-bolt 8.5's going to use the same cover and if not, how do I know which one will for sure fit before I order it?
Since your going to take it off, I would drill into the bottom of the housing and tap it for pipe plug. Cast iron drills and taps easy. The larger the better depending on the thickness where you choose. 1/4” would be my minimum 3/8” better. Make sure you are in an open area because the tap and drill need room. There are Allen socket plugs at Ace hardware that would be flush. I would also epoxy a magnet to the bottom of the plug.
I beleive all 10 bolt 8.2 and 8.5 Chevys take the same cover, if you can, spend a little more for the aluminum cover with the bearing cap support like the Proform perfect launch #6668
The 8.2" does not use the same cover as the 8.5" 10 bolt Chevy differential. But Nova, Camaro, and Chevelle 8.5 will all use the same cover. https://www.chevydiy.com/history-and-identification-of-chevy-10-and-12-bolt-chevy-differentials/
Thanks for the info. I'm going to pick a cover that has a drain plug so I won't need to drill the housing. I am not sure I need the bearing cap support since the engine is only producing about 120 hp (which is quite a bit more than this thing had stock) but we'll see when I place the order in the next month or so since this will be an end-of-season fix. The less "flashy" the better as the truck looks mostly stock and the diff cover is very visible. Boy, though, just about every cover has at least one complaint about the bolts being too short!
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