I'm not sure about the 9 or 10 hole deal... but I replaced center section my 51 GMC and picked up the Felpro gaskets at NAPa, they fit and worked perfectly.
info here:
https://www.stovebolt.com/techtips/axles/1%20Ton%20Upgrade/

Differential carrier gasket: Felpro RDS5090 (the thin one)
Rear diff cover gasket: Felpro RDS5088 (the thick one)

I would not use RTV or similar instead of the correct carrier gasket because the gasket thickness is planned for good alignment of axle shafts into the side gears.

Here's the step by step of changing my gears.
https://www.stovebolt.com/ubbthread...ve-improve-drive-repeat.html#Post1141931
Sorry the picture links don't work... here's the album https://photos.google.com/share/AF1...UldVQzUxVkl1ZnNKN25yN0Q3UFpWcWN4blhmVXVn

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-