As long as the engine is serviced as required and you let it warm up properly before you boot it, it should last many thousands of miles, there is always the odd one that will let go sooner rather than later but generally they are a reliable engine
In the for sale sections of all the major forums or ebay
Keith Michaels is generally the best as they will cover mods but you have to be a fully paid up member of the SIDC to get the full benefits
Deano 666 on here for most work, he is used by many of us (including me) and can come to you if needed, also Kent Performance seem to be doing some good work lately, as for track days have a look in the track days & national events section on this forum