1970 Engine replacement

[JoeKan]

I have an opportunity to get a real nice looking 1970 Camper Special, it has some rust but not bad. The bad thing about this is the motor is shot. The owner said that it had a busted head gasket and let it sit for awhile before attempting to fix it and water had gotten into the piston.
I don't know very much about motor overhaul or replacement but can someone give me an idea of how big of a pain in the neck it would be to do this myself (with help) or how much it would cost if I paid someone to do this?
If I would be better off getting someone to do this, then who? "A" mechanic down the street?
I would hate to walk away from this because it's a good buy and I want to restore this old girl. Thanks for any help, Joe