I would not feel at all comfortable getting a price concensus from the peanut gallery on something like that. I'd head straight to the SWCA and, if possible, give them a SN.
I might be wrong on this, but I did not think Smith Wesson did factory engraving on non-steel (alloy) guns, back in the 70's. Like I say, I might be wrong.
i couldn't give you what you would want for it.....
im trying to firuge out what to ask for it.
when you find out pm me maybe we could work something out....very interested!!!