GM used the 10 hole Motor Wheel hub for a long time after 55 and not all of them were the the the Firestone design. 6 Hole stud piloted was an option. Many of the were the Goodyear design had a lock ring and there was also a 3 piece design. These wheels will take either a 7.50 or 8.25 x 20 tire which is readily available in the US. There are a lot of old GM bobtails in barns in the Dakotas. I don't know if there are are still any border crossings there with no customs. I haven't been there in quite a while. Quite often a whole bob tail field truck with 6 servicable wheels can be bought for less than $1,000 and the cab will fit a pickup.