With bent valves you wont know how much of teh engine needs to be rebuilt until you pull it down. You may be lucky and need to just replace the valve, it kind of depends on how bent they are. I am rebuilding an '86 for my nephew(he is learning how), and the truck also suffered a broken t-chain. After puling the head off/down, only one valve was slightly bent, and there was no damage to the piston other than a very small nick in it. Others I have pulled down that had trhe same t-chain failure had large chunks out of the heads, requiring new pistons and rods. If you only have to replace a few valves, pistons, head, or all 3, either way for $500 it is a good deal. You should be able to rebuild it for about $500, check enginebuilders.com for a rebuild kit.

It may only have 50k on the clock, but the chain is 18yrs old , and probably has a lot more hours(revolutions) on the chain than the an average car here on the mainland would w/only 50K.