Hi Sundancer, welcome to flathead central!
A picture would be worth 1,000 words as the old adage goes.
Without that, almost all the cast numbers on flatheads mean very little and don't help in id'ing.
Heads only marked 36X are likely aftermarket and not much help
Just saw your post on fordbarn - no integral bell is 48 - 54 US/CAN
Anything aluminum? Intake? 3 or 4 bolts where the carb bolts on?
Not much in the way of parts differences in that run - I just order parts in the middle eg.1950 Ford V8
Only significant difference is the 3 3/4" vs. 4" piston stroke.
...they were right.....the world is flat!