There were 4 models produced in the 50"s. The silver muffler is not enough information for me.
There were 7 variations of the H, 2 variations of the M, a 400 and a 450 produced in the late 40's and 50"s
A picture would be worth a thousand words to help identify which one you have. In good condition they range in price from $250 to $800 depending on which one you have. We can probably eliminate the 400 and 450 cause they came out in the late 50's.
Tell me more or post a picture if you can.