Hi Steve They are very likely to be factory castings just from the appearance. Scotts cast in the ports with a ridge at the top where the exhaust and transfer meet the bores. They were set up to ledge on these ridges to get the porting timing correct without having to machine in the ports.
I do have a works drawing of this I can send you if you email me. The blocks are not easy to cast as the thin inner core for the water jacket has a habit of coming detached and floating around in the casting process, although you get more success if you cast upside down
I do have machining drawings if you fancy a crack at it, A time consuming expensive job but certainly better if you do not have to machine in the ports as I do
Kind Regards
Roger
