I ordered a HCV for "55 - 57, will also fit 58 - 50." Yeah, it FIT, but the nipples weren't like my original. It leaked before the year was out. The way I recommend dealing with your problem is to return it for a refund.
I don't remember having a problem between the valve and the core. I was able to get that little hose (IIRC) from an aftermarket supplier.
But to answer your question regarding how I compensated for the difference, I jerry-rigged it by getting an adapter and a couple of hose clamps for each side of the HCV. I don't exactly remember the sizes involved, but (for example) I attached a 5/8 hose at the HCV and ran it out the firewall, then clamped on a 5/8-to-3/4 adapter, then ran the 3/4 hose to the water pump.
It looked like crap but was functional...until it leaked in the cab. Then I cut the hoses at the firewall and put in a loop at the water pump. I'll replace the HCV with my original one after rebuilding it.
Good luck!
Bill
