H box. I was assuming it is the linkage assembly on top of the column just in front of the firewall. Is your '50 a stick or auto?
If it's a stick, just take a look at it and compare to your '48. You should be looking at this stuff anyway, since you will need to know if the '60 will work or not. Unless someone can tell you for sure the '60 stuff will work on the '48 column, you're gonna need to figure it out yourself.
Make sure you measure the rearends before buying. Don't want to do it twice!
