so Matt is it all sorted, is the GT back on the road ?
Apologies for the late response - having started this scary thread I should have posted a final update earlier. Yes the GranTurismo was back on the road by late 2020, replacement engine as good as new. While it was with Matt they did a thorough check-over and everything else that needed doing was done, including new front suspension bushes, various gaskets and underseal. It drove beautifully, and I am very grateful to Matt and Ash for sourcing the replacement engine (not easy) and completing the work to a high standard. Their evident expertise and attention to detail, plus excellent communications throughout, were very reassuring in a sometimes scary situation for me. Plus they obviously saved me a ton of money compared to a factory engine replacement.
I sold the GranTurismo in June last year, mainly because the roads around here (Norfolk, farming country) are dreadful and I didn't relish more bills for pothole-inflicted suspension damage so wasn't using the car much at all. A Range Rover V8 diesel on all-terrain tyres is certainly more usable around here, if not remotely as much visceral fun of course. I havent ruled out returning to the Maserati or possbly Alfa fold sometime - I can't possibly be that unlucky again - can I? Thanks everyone who responded to this thread for your interest, sympathy, help and encouragement, it was invluable.