Yes you definitely want to use it if it checks out OK after inspection and the machinist can deck it clean, especialy since you already own it. If the decking brings the pistons to zero deck height , that's a bonus in my opinion, as long as the manifold fits afterward. Wont be able to tell what you have until you take it apart and thoroughly inspect it.
As far as the aviation sealer, stock or not I wouldn't use it to seal the heads, but that's just me. Just my two cents and opinion, others may disagree.
see, out by me (near the shore) JB weld (shivers ) and Aviation seal are used frequently to fix blocks chewed up by salt water in boats. some of them you'd think were toast as it looks like someone spooned out some metal and these guys go and run the crap out of them for 100's more hours.
if this block has never been machined, what do you think is the max I could take off of it? i sent those exact pics to the machine shop and they think .025 would get it to where the pitting is like its not even there.
) and Aviation seal are used frequently to fix blocks chewed up by salt water in boats. some of them you'd think were toast as it looks like someone spooned out some metal and these guys go and run the crap out of them for 100's more hours. 
