Re: C and C Mk2 portlights
You'll have to check the Lewmar catalogue and know your existing port dimensions, and probably have to pick the next size up. This might be a difficult job because IIRC the MKIIs cabin has a fair bit of curvature.. Opening ports will only tolerate so much before they won't seal properly and the lenses can be under stress when closed.
It would update the boat considerably, though! Another option might be to simply replace your lenses but put a small opening port into the lens itself if its big enough, that would provide at least some cross ventilation and mean less finishing work as well.
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)