Hi Mark,
I own BEF2545 which has been completely apart and is now going back together. It is the car with Mike Engaard at Ragtops. We found the chassis number in the following places:
(1) On chassis itself, top of front shocktower on right side - on the lip closest to the engine (might be on left side if LHD car) - full number BEF2545.
(2) Stamped on the wood frame in the rear trunk lid (I believe number only, e.g., 2545).
(3) Hinge in hood (bonnet for you in UK) between bolt holes - number only.
(4) In pencil on the back of at least two of the door cards and other trimmed interior components - number only.
As an update to the above conversation about brake drums, I was speaking with Crossthwaite and Gardner (I know them pretty well from other projects) and they manufacture the drums but don't sell them directly - you need to contact Mr. (Mark?) Finburgh of Classic Autos of King's Langley for purchase for Ace (01923 262994). Apparently,they are now out of stock at C&G but Finburgh may have some Ace drums on the shelf. However, since they are OOS, C&G will soon be making a run of Ace drums. If you want these but with the Greyhound PCD or undrilled, then contact Finburgh and maybe he can run some with the others. As stated above, no one uses pure Alfin process to manufacture the drums.