[will slow gto]

The YS block was installed in 44,000+ 1968 GTOs so not a rare piece. There's a guy on here selling a standard bore YS block from a 70 for $600 so that gives you ball park. #16 heads and the matching intake manifold aren't rare either. If I was me I'd ask the owner if he would let me take block and crank to a machine shop to see if they will clean up at 0.030 and .010, respectively. If so, and the heads are in good shape, AND the casting dates were about two months prior to my vehicle build date, I'd offer $1000 for everything and work my way up from there based on condition and how eager you are to get going on it.