To make a decent call, we need more info.
a) pictures
b) far more detail on parts installed...
c) status of the car's title (Is it salvaged?)

Also, when you say he has built the car to race it... in what field?
And what are your goals for the car?

The general rule is to never buy someone else's project car, unless you understand the risks and potential expenses involved in re-doing things the right way. And there are some modifications for racing that just don't translate to the street (such as a fully caged interior and fixed back racing seats).