Early 8 3/4's, with two piece axles, do have different lengths between SG and non-SG applications. But that's not what the OP has (I hope).

What sure grip do you have , the case don't matter unless you know for a fact that it has never been messed with .

489 would have come from the factory with a Cone type , no buttons , just a thrust block that can't fall out.

Clutch type has buttons and they can fall out when the axles are pulled, the roll pin is an assembly aid , after many thousands of corner turns it will eventually break , it's not a potential problem till an axle is pulled.

What sure grip does it have ?

It came out of a 1971 cuda - 3.55 - unmolested - 489 case

Different length axles for open and SG are 1964 and older with the tapered axle & nut.

Then it's a cone type ... No buttons, just a thrust block that can't come out unless the sure grips is completely disassembled.