Gemma, please be very carefull.. a properly done rebuild costs £Â£Ã‚£s, and unless you go through the whole engine with a fine toothed combe its really not worth doing  Im sorry , but you have to question the wisdom of this man, the only guanantee you have is that if anything goes wrong, this guy will fix it free of charge!!! and he's got to buy any new parts that may get damaged.. I would steer well clear, it's not worth the hassle, the money, the time and the greif.
Find yourself a second hand engine, from a reputable salvage specialist, i'm sure that there are enough people here to help you out in that department, get it, put in, and enjoy your car!, it will only cost you money!
Tom