hey Kyle! welcome to the 'bolt, a great place to find out about yer new truck! unfortunately, how many of any particular option were produced isn't one of the things you'll find
just depended on how many folks ordered that option, and GM didn't keep that type of record until the late 60's - the hydromatic is uncommon tho' - one of the best sources for production info is the Standard Catalog of American Light Trucks, but even there the breakdowns for the 50's is just total light/ medium/ heavy trucks
another spot you might check that's aimed at GMCs in particular is Robs
old gmc truck site , tho' they're more heavily into the earlier years
Bill
