Highwayman,
Don't know for sure, but I would imagine your 38 would be set up similar to my 46, (with a 1939 216 and original 4-speed and rear-end).
At any rate, my truck will cruise comfortably between 45-50, on stock 16" wheels/tires. It'll run faster, but I don't do it for any extended period of time.
Hope that helps.
