Welcome aboard fellow Iowan. I go to local truck repair shops and power train shops. If you're anywhere near Cedar Rapids try Sadler Powertrain. I just got a hydro-vac from them last fall for a 48 4400. A lot of truck parts are the same for many years.
Good luck,
Scott

Scott Ward

2 1948 1.5-ton Loadmasters
The red one and The snow pusher
1 1950 3100
1 1955.1 Chevy 6500
1 1954 Chevy 6500 2-Ton
1 1955 1st Series COE 5700
1 1963 K20 (454)
1 1964 C10 (350)
1 1951 1.5-ton Dump Truck
1953 and a 1956 Ford F800

Raising a teenager is like trying to nail Jello to a tree!