I'd say it would cost approaching 3x the asking price to build a car to a similar spec.
You're correct in that MG only built the MGB V8 in GT form until the later RV8 came along. An engineer called Ken Costello was one of the first to start turning out V8 engined MG's and, it's alleged, his cars prompted the factory to look more seriously into making a production version.
There should be no issue with overheating if the modification has been well executed and there is plenty of information and equipment available to assist in same.
One of the attractions of MG's is the availability of spares, upgrades and information that is readily available and affordable. Even the V8 modified cars are well catered for by the clubs and the specialist suppliers.
That book and that car were my guide when I converted my roadster. So it’s been done for 30 years, I’ve seen it at the NEC and it was a very nice car 20 years ago. I think the MAF is a flapper which is unobtainable and not repairable either (I think). I’ve driven an MGB with those suspension mods too, felt uncannily modern.
