Interesting. If anyone would like a hand getting this to work, I spent some time with my friend Rich J getting his Island twin turbo system up and running (before we converted it to a bona fide 2.5 turbo engine). £250 is reasonable but I wouldn't pay much more - you could make the same thing with a donor turbo and some simple pipework.
Check if it's a T34 or a T3/T4 as the latter would be a bit big.