wheel/tire fitment tool question.

[spinedoc]

I am going to attempt to purchase new wheels/tires fro my 70 camaro. Stock axle length, DSE mini tubs, ridetech 4 link.
I see there are variations in size among manufacturers, even among the same listed size.
I see the tool that allows you to mount a tire and calculate BS and size. Does anyone have one they would want to let me borrow/rent? I am sure I am still capable of screwing up the sizes, but this may limit the size of the fiasco
Thanks,

Eric