Dinnette was not a retrofit
It was standard on that year. The 76-81's had some differences then the later models including dinnette (convertible to large bunk) , solid fibreglass hulls, upright built in fridge etc
I have a 79 and I love it. In the process of refitting it.
One thing I will say is its easier to handle then you think. I had a 40' rear cockpit sailboat prior and I find sitting in the center cockpit gives me good visibility bow to stern.
In regards to work shop there's a cabin to starboard ahead of the salon with bunks that you could use or of course the dinnette...
The prices on these boats now are fantastic if you dont mind doing some cleanup. I would not be interested in purchasing the one that partially sank thats been out there however unless is was at least half the other prices