JP,
The Chipmunk is an excellent aeroplane to lead tailwheel with, and £140 an hour does is not a bad price at all. It is an expensive aeroplane to run, especially on a transport category C of A, in which case you do not get a lot of engine life (I think it's only 1000 hrs TBO) and this makes the hourly cost expensive in a commercial operation. Only thing I'd add is that it's a really good idea also to get in some good dual instruction on a type with a less forgiving, narrower track, bouncier undercarriage, e.g. a Super Cub, of which there are quite a few around to choose from. And at some stage I would heartily recommend that you get checked out so that you can fly comfortably and safely from the back seat of the Chipmunk as this then simulates the lack of straight-ahead vision that you get in lots of tailwheel aeroplanes (The Chippy, Super Cub and various Champ derivatives while all frequently used for tailwheel training all give a much better view ahead than most tailwheelers, and you will find the experience of something more "blind" stands you in good stead if you ever have the chance to try other types, e.g. various Permit single-seaters)
CB,
If I were rich enough to afford my own Gipsy-Major powered aeroplane, I would want it to have an engine rebuilt by Vintech at Little Gransden. A quick Google search will get you contact details. I am sure they will be able to give you a ballpark figure. But it ain't cheap. I have around £25K in my mind, but may well be wrong so I suggest you give them a tinkle.