I can't believe that nobody mentioned the brakes yet - the single biggest reason I wouldn't start with a 220 car as a project is that it will cost £££ and hassle to get decent brakes on it. By contrast the 250 has bigger brakes already and you can just bolt even bigger ones up if you want to go further. It's only a week since we've seen RUMS944 struggling to get bigger brakes mated to his early 220 car.
Apart from the brakes you also get your LSD, bigger turbo, stronger 1st and 2nd gears, gearbox oil cooler, thicker drive shafts, ARBs etc.
I agree you should buy on condition, but I don't necessarily agree that a good 220 can be had for £4.5k and an equivalently good 250 will be £7k - there isn't £2,500 in price difference between them IMO and the difference in spec is worth the small premium. OK the early 220 might be a bot lighter, but if you're interested in weight so much you'd delete worthwile performance kit to go light then buy a Lux. All the alarm and 10 speaker stereo tat can be taken out and some of it will sell on eBay to offset the extra you paid.
Tired M030 is worth nothing compared with tired Boge suspension and I wouldn't pay a premium for a car with rebuilt M030 as it isn't all that as has been said.
I used to know this car http://www.pistonheads.com/sales/209525.htm and apparently (I know someone who looked at it) it has some issues that keep the price down, but they are cosmetic in the main and it's available for less than the sticker price yet it has the 250 spec plus, level 2 kit already and Janspeed exhaust (full system, not cat back as the owner seems to believe) etc. already fitted. I'd need to see how the sills look to wholeheartedly recommend it, but it looks like a decent track prospect to me.