To update my situation:
Many thanks for all the useful information and warm encouragement on this thread! Based on the postings here I went ahead and purchased the 503cw, together with some good used lenses (100mm and 180mm). Sure enough, it's a great camera, and I look forward to decades of photographic adventures.
Again, my sincere gratitude for helping allay my qualms. I might have missed a precious chance to acquire what may well be one of the last V models made by Hasselblad.