Fabby is way down in Devon so that may influence your choice.
the Fzr bike is a nice bike with a very strong motor, i,ve raced a few, the bike you have been offered is ok, but if i remember your original post the bike isn,t a runner at the mo????
maybe suggest to the owner that if you or him can get it running then it may be worth it for you, its not a bad engine but worries me its not running at the mo.
the kwack engine isn,t as free revving as the Fzr but has good torque so in a car it might still be a good choice.
has he said £300 for it? if so offer £200 as a non runner (subject to why its not running etc) or £300 for it if he gets it running.
sorry i know that doesn,t help much but thats what i would do,
cheers
andy
ps.. its ok, i dream of my bike racing days too, smiles