It's the motor/hp size you want to know. If you can find a model number a web search might throw up info. Or a sticker on the comp. Rough rule of thumb, 3cfm FAD for every 1hp. So you probs want 2hp+ as most masks seem to want 6-7cfm or more. Note its the FAD you want to consider not the displacement.
With linking, when I did similar on mine I had to adjust pressures on the big chap (also 14cm - displacement - about 9.5 FAD). Big fella cuts out at 150psi normally, which is blow-off for the little one. There's info on here on linking comps up, worth a nose.
Thanks Chipper. Today I picked up a a second hand but un-used 3HP Clarke Raider 60 with 14cfm. So I should have about 19CFM FAD now - will have a read up on connecting them together now.
I have been looking at masks on the net, some of them now seem to want a min of 4cfm, so 5 or 6cfm should be enough for the mask without joining the two compressors, but im no expert.