First off, Nice car.
Not much to pick at except things that were already mentioned like disc brakes are a must. Are you sure you want to drive a Non-A/C car in our incredibly hot and long DFW summers? It all depends on how much you plan to drive it.
The vinyl for the top won't cost much. Probably under $100 but all the trim pieces in nice shape can cost you another $100 - $200 and hard to find. Labor will probably cost about $200. I just got a quote for installing a headliner in my 69 GTO and I would supply the full kit and it was $275 labor here in Plano. I guess I'll do it myself
If you are ok with his price and the fact he said he wouldn't budge, then I would tell him all the things he needs to fix to fetch that price from you. I bet he would then consider lowering the price.
I didn't see anything about the block being rebuilt and when/who did the work and is it documented well?