First off I think that it would be false economy to go though all that hassle when you could probably buy a nice used 5 shot for less than the cost of modifying yours.
BUT I've done enough things that didn't make sense in my live so I won't critisize.
Second. The older M37's had a barretl that "turned" out opposite of what the new ones do. Sorry but I don't have a serial number that the change took place although I do know that the older ones are kind of hard to come by.

Reiman:
Thanks for the info. You are probably right, may not be an option.
Regards,
hm

I have a Mod. 37 eight shot riot gun (SN 371,***,***) that I would like to put a standard barrel on. Thinking about changing out the magazine tube to standard length and looking for a used barrel.

Are all (12 ga) mod. 37 barrels equal (other than mag. tube length) or are there differences?

Thanks,
hm