8 3/4 swapped in but....thrust button?

Hellooooo FABO!

5 yrs ago (maybe 6 now) when I rolled this puppy into garage, I did a mini tub job for the '70s' theme hot rod and wanted a bigger tire out back as I feel these fastback have a big booty and wanted to even out the look with a big tire. I found a already narrowed 8 3/4 with a 3:91 sure grip and it was pretty close on width so thats what im using. (Yes I saved the original A body 3:23 sure grip with brakes and parking cables...) I dont remember a thrust button when I went through this thing. It has stock style bearings. I am getting closer to being able to take it around the block minus glass and interior, I might be able to 'roadkill' it for testing purposes. Since I cant be absolutely sure it has said button, Do the FABO Gods recommend a pulling of chunk, sliding out of axles, and checking for button? If the button doesnt exist, and the axles are butted up against each other.....or very close to each other...whats the fix? I just dont get how that button has any give to it to affect adjustment. the outside bearing have to be tight against the races ya? So I will pull chunk, slide axles back in, and measure space between them to 'cut in' the button? I have snooped around for the answer, but I am not getting the purpose that button provides as far as any adjustment or stability.

Please pardon my ignorance as I know this has been covered.

Thanks fellas!!

My darlin Clem.:)