HA-HA.... a 1974 "H" would be a FARMALL 544... was a real nice diesel w/ wide frt end as the cover tractor on the last issue of RPM.
I don't think a CC in decent shape would have a problem with 50 miles. I'd do something like Lonnie B does, put some taller tires on the thing, plus maybe over-drive reduction gears. You'd maybe have to have a spare gallon or two of gas. A gear drive would be the way to go. With 3-1/2 quarts of Hy-Tran splashing around there shouldn't be any over-heating problems. And the stock frt wheel bearings would be fine. Anyone ever figured up how many miles they drive mowing their lawn?
BILL J. - Lucas is correct. I used the flywheel, blower backing plate, & flywheel enclosure off the K301 in my #129 on the K321 to drop it into my #72. I didn't want to cut up the frame on my 72. I will say one thing, the K321 gains RPM like a Formula 1 race car engine. And the K301 that got the bigger flywheel, ect became a slug. Still pulled good, but was slower to gain RPM.
Over-all, the K321 in the 72 has been a great performing tractor. IH never made a GD over 12 HP, but over doubling the HP of the 72 hasn't caused any problems what so ever. The extra HP is really nice when I run the lawn vac. Pulling the tractor & mower, plus the vac unit, plus a cart full of clippings or leaves was more than a 10 HP could really handle. I'd guess the total weight of the loaded vac was something around 2000 pounds.