Checked both of my Weber reference books, can't find any DCOM designation.
DCOE is a 2-throat(barrel) horizontal die-cast. The last letter can stand for anything from type of material it was made from, to the fact that it has a water-operated automatic choke. Sorry, can't help you with the M.
I'm very wary of any used webers since outfitting a set to work on a different car than they are currently on can cost more than new ones.Primary venturis, aux venturis, emuslsion tubes and jet package should all be considered along with overall condition.In order of listed above here's where I'd start with a L-24,24-28mm primary venturi,3.5 aux,F2,F11,F15,F16 emulsion tube.As far as a jet package this vary so wildly I won't give recomendations.Besides it's not really important since my point is that if these carbs are'nt close to begin with then figure about 30 dollars x4 for primary venturis 20 dollars x4 for aux 16-18 dollars x 4 for emulsion tubes ect.This is assuming you can get parts for a DCOM.Buyer Beware on used Webers.