I think you're asking a question that's impossible to answer using the internet only, especially without pictures. Have you had a look at the truck in person? What's it worth to you?
I figure that unrestored 88s in the condition you describe would be in the $3500 to $8000 range.
Pretty wide zone, eh?
1967 NADA 109 is a collectible, eh? Well, I don't know that it's any more "collectible" than any other 109 (or 88 for that matter).
88 Safari tops are around. Roofs in general aren't too expensive--That's because nobody can get rid of roofs because nobody wants to ship roofs. They practically give them away because it's pretty much a local-pickup thing. It's just a matter of finding one with a sun sheet locally.
--Mark
1973 SIII 109 RHD 2.5NA Diesel
0-54mph in just under 11.5 minutes
(9.7 minutes now that she's a 3-door).