That has got to be one of the nicest restoration jobs I've ever seen on a MGB-GT.
I found it interesting they said the engine was a true "Buick" built engine, instead of the later "Rover" built block, and it was arguably, of better aluminum quality.
Buick designed and built that engine in the early 60's, but always had problems with it's water passages "shedding" aluminum, and clogging up. Which in turn caused the engine to eventually over heat.
In typical GM fashion (back then), instead of working out the problem they simply sold the licensing "rights" to British Leland to manufacture the engine.
They got the "shedding" problem worked out, and continued to use the engine in Rovers, MG's, and Triumphs for years.
When the fuel crisis hit in the early 70's, GM didn't have a light weight economical V8 to install in there up coming "Monza" based compact car line. So they went back to British Leland to ask them if they would be willing to sell the licensing rights back to them. British Leland declined, but did offer to build the engines and sell them back to GM for some outlandish price which GM of course turned down.
That's when GM decided that their old 231 cu.in. V6 wasn't such a bad design after all, and started to develop it for it's eventual availability in practically every car GM offered for awhile.