I'm looking for any information pertaining to the Spitfire SMG.  

I understand an M3A1 bolt is a popular upgrade.  Anything else?

I've had hands on w/3 different Spitfires and have these notes.  There's also a Yahoo group on this gun.

All Spitfires declared as MG so if not registered in '68, they are just parts kits.

Came in short or long barrel, w or w/o vertical grip.

Mag catch can be square or D cut so some M3 mags will not catch.  Easy fix is to make it square so works with all mags.

There is a sheet metal feed ramp which some guns don't have but does not affect function.  Others won't run w/o ramp.

M3A1 bolt needs mod as well as tube mod for function.  Serial number is on the cast lower/grip.

M3/M3A1 recoil springs work.

That's a nice start. Thank you.

Well, I bought it.

Time to start scouring the internet.

I'd like to either convert it to 9mm, or build a new 9mm upper.

Good for you!!  And welcome to the Spitfire club.

I would not build a complete 9mm upper as it's iffy legalwise.  There is an ATF letter out there stating that the Spitfire upper tube and lower housing is the combination of parts making it an MG.  Just adapt a 9mm bolt to fit the existing tube.

Look at a Suomi M31 9mm bolt as donor or the newly produced M3A1 9mm bolts.

Interesting.

Are the Suomi bolts somewhat close in size?  I know the m3a1 bolt needs some minor welding on the sear engagement surface.

The M31 bolt is much smaller in diameter so that actually makes it easier to rework.

Indianapolis Ordnance is selling newly manufactured 9mm M3 Greasegun bolts......one of those, a bbl, and a sheet metal adaptor to use Sten mags and you'd be good to go.....

I've been watching those.  Waiting for threm to restock.

I was able to find a complete M3A1 bolt/recoil assy.  Ordered.