I have Mango number 46 from 1985. The Mango is a great boat and IMHO (I know this will be controversial) the best design that Henry came up with. Yes, they are older boats but if they have been maintained consistently and well and not extensively modified they are great cruising boats. I have lived aboard mine now for 3 + years and she was and still is in pristine condition and has been a great boat. (ok the hull needs to be painted)
So having said that, Yes a Mango in great shape is a solid boat. However any boat that has been neglected should be avoided. Hire a good surveyor that knows these boats, and go into it with your eyes open and with as much of that particular boats problems identified. Any 53 foot boat can be a money pit during a refit and repair.
An easy way to rule out a potential boat (before hiring a surveyor) is look at the wiring, bilges and the engine room. If they are not in near perfect order, I would avoid looking any further into any vessel that fails that initial sniff test.
Just my 2 cents from a Mango owner.
1985 Mango Hull # 46