I had a chat with Mike Vaisey from Vintech recently and he was saying that Gipsy parts are getting increasingly hard to find, especially exhaust valves. Chippy exhaust valves (sodium cooled) are 220 quid plus VAT each, so 4 of those, the most basic bits of a top overhaul cost you a grand straight off. OUCH. Cylinders, pistons and rings are also getting scarce. Unless the CAA ease their attitude on replacement parts being manufactured by reputable companies not necessarily the original manufacturers, Tigers, Chippies, Austers etc operating on a C of A are going to be grounded in the not to distant future unless they are owned by millionaires......
Rant mode off, back to topic.
Budget a chunk of change for an overhaul, around the 15-20k mark depending on the condition of the engine to be overhauled.