Rebuilt 318 Magnum. Is it a good deal?

Seems reasonable. I think your power estimate is a bit high. Probably more like 330-340, but nonetheless, a pretty decent deal.
It may be a bit high, but it very similarly follows ‘hot rods 400 horse 318’ build, but roller rather than flat tappet. Some pocket porting/ cleaning on the EQs and i feel it’ll be plenty stout. Besides, if i ever decide to go 5.9 Mag in the future i’ll have the perfect heads for it.