53/54 uprights are 1/2" lower than 49-52.
There are a few place that sell dropped units. Nationalchevyassoc.com, chevsofthe40s.com, and fatman all have them.

Check out the links page on 50chevy.com theres alot of useful stuff. Actually, check out the whole website. Its the best I've found yet for these cars. Tons of pictures too.
Good luck.