Hi Sean,
SRM list both size inlet valves 67.1551 and 1.5in 67.0961 (SRM215 )
It takes very little seat cutting to accommodate the bigger valve, so if the seats are in any way pocketed the bigger valve will be fine
Last week I was working on a 52 Star twin cylinder head where the seats were pocketed and the exhausts fairly pitted
After cutting the seats just enough to get a good surface the original valves were well recessed
Options
fit seat inserts ?
live with it?
find some larger head valves?
A trial fit of an A10 exhaust valve looked good, and the heads could be reduced if necessary?
Yesterday the new A10 valves arrived and a quick lapping showed that they were seating nicely and no machining needed
I will need to check clearances between the valves and valves to pistons but I do not anticipate problems
The Star twin head inlet ports looked quite different to each other ????
One looked to have very little "meat" behind the seat area to support a seat insert if one was going to go that route
Maybe those odd ports are a reason why some BSA's show cylinder bias
John