Advice on engine rebuild

I've had my '87 5.0 sitting in my garage since three years ago when I blew the head gasket. We recently started to rip the engine apart to make sure it was head gasket and to try to fix it. The compression test was OK on cylinders 1-4, but 5-8 showed something definitely wrong, in fact cylinder #6 didn't even register. Well when we pulled the heads off I did notice the gasket was blown; however, we also noticed the gaping hole in the piston #6 (detonation?):


My question is what is the most budget friendly way to go about fixing this? Is it possible to just replace that piston or do I need a new long block? I've already bouight a fel-pro gasket kit.

thanks

The motor did run after the head gasket went, it even started three years sitting in the garage. I've contacted a mustang junkyard already figuring I'd have to replace the whole block. Here is a picture anyway...



thanks!