Heater hose fittings for 351C

No wonder you can't find them, you're looking in the wrong places. Just run down to your local parts house, they're all there. The one for the block does just press in, the W/P one screws in, has very common NPT threads, 1/2" NPT I believe. Even these can be had at any Lowes or Home Depot store.

Don't feel bad. I remember it took me a while working on my families' daily drivers to figure out which parts I should go to the dealer, versus the parts store, versus the hardware store, etc. Sometimes it still surprises me, it's worth an extra telephone call or two to check.

Sometimes the dealer can be cheaper than the discount parts stores.

Although the Cleveland was killed here in the U.S. in 74, the 351M and 400 stayed on in production til the early 80's. They both used the same fittings the Clevelands did. But there were two sizes for the pressed in fitting in the 400's ( at least) one is 5/8ths and the other is 3/4 into the block , necking down to 5/8ths at the hose end. Just about any part that fits a Cleveland is available at most local parts stores, this is also true for many other Stang engine, drivetrain, and suspension parts. No need to go mail order.