Have someone who is really good with heads look them over very thoroughly before handing over any $$$.
They can easily cost too much to straighten out to be worthwhile.

As for chamber volume, the only ones I recall actually being close to the 78cc spec were the last version from the Zeus foundry. The others were all over the place...... Up to around 92cc's.

IMO, they would have to be priced VERY attractively to be worth messing with them, unless you have the capabilities to do most of the work yourself.