Update.
Kiwi mentioned making barrels for A10. Could do, but.... Pattern making and core boxes would take about a week. Dunno what casting costs are these days as I've not had any done for 3 or 4 yrs, but I'd guess around £100. Then there's postage, machining, purchase 2 x CI liners, fitting same & boring / honing to size. Not sure about cam followers - might mean a bronze insert (have forgotten how they fit). Total cost probably north of £400. And what's the demand with a reducing number of bikes / mileage? 10? 100? Last of all, I no longer run my business, so there'd be no insurance against a claim that my cylinder caused a rider to crash etc. So not overly interested.
As for cylinder heads: the engines I've made so far do not represent a make - my first was going to be a vee twin B31, but when I discovered there was insufficient room for 4 x BSA cams, I decided to go for a 'my engine using B31 heads & barrels'. The second one was never intended to be a vee twin anything. It was intended as a race engine and it just happened that Yam XT heads offered the best solution.
I know from experience gained thus far that, because I have no intention of designing my own heads, a suitable head sets a lot of parameters for the other parts. So head choice comes first.
Over the last few days I've examined several possibilities. On the OHC front, only Yam XT really fits the bill but, as mentioned previously, that would mean making a copy of what I already have. A few minor upgrades, but otherwise the same. So no point.
With OHV, BSA's are either not suitable or too expensive. AJS / Matchless not really suitable (usually their inlet port is too far the the right, meaning a dog-leg manifold to get the front cyl carb away from the rear cyl exhaust). Also, there's an inconvenient recess where the barrel sits.
All that really appears suitable is Enfield though, as previously stated, I'm not impressed by their crude rocker arrangement. That said, I'm pursuing the purchase of a Bullet head for analysis before proceeding further.
On a sadder note, I had been making enquiries about my late friend George's machinery, seeing as how I used to rely on some of his gear (eg pantograph, cylindrical grinder, heat oven etc). Just learn from a mutual friend that George's dopey sons (believe me, they are seriously weird) have 'disposed' of it all. Apparently for no consideration!
PS - And that was a fair bit of gear. 3 X large pantographs (one 3 axis), 2 x surface grinders (one weighed 5 tons or more) a large slotter (again, several tons) a Russian metric lathe - several tons again, cylindrical grinder, spark erosion machine, Beaver and other mills, heat treatment oven etc etc
