Hi Dave, reckon you've had more Connie-owning experience than me then, I've only had mine long enough to do most of those mods and a few thousand miles, still with minor oil dribbles despite best efforts. I like it well, but not the easiest beasts as I said. I'm running Boyer ignition, a regulator from Paul Goff on a big single phase alternator and the original twin Monoblocs with the rh one chopped and bottom-fed. If you've got piston issues, then hopefully sorting them will eliminate your pressure problem, especially if you do domething about the drive side crankcase disc breather. Under no circs should any original breather venting the crankcase into the primary case be retained if you've got one - my RE mentor and guru told me of three major disasters caused by the explosion of unburnt fuel in there, one of which destroyed the drive side crankcase, the others of which 'just' did for the chaincase. Don't quite know why, as my AMCs vent happily via flapper valves in their drive side crank axles, but 'tis certainly true nonetheless - and decent castings are parts that aren't easy to get.
Hitchcocks is the standard by which I have been judging all other suppliers these past few years - I'm sure you'll have no hassle. A local non-English speaking friend is restoring a Super Meteor so between us there has been a massive traffic in parts through here, and not a single problem, with new or second-hand bits. Very Impressive - and also of course for most things Amal.
Be very interested to hear how you find it compared to the very excellent A you have got. Personally, I find my A smoother and easier to ride, vastly better transmission of course, and that it is just as quick A to B for most purposes. My Connie, which is a typically uncomfortable café-racer, has short roadholders per later Interceptors and a tls Commando brake, so it does actually stop better by far than anything else in the shed. That's it's strongest suit, along with being pretty if you like that sort of thing!