I have built several race Mgbs and Mgbv8s which handle a sight better with poly bushes and have run two Alfa Romeo 156 sportwagon s, one quite modified, which have had every single rubber bush replaced with poly bushes for over a decade: again, a vast improvement: simply put, the replacement of rubber bushes with poly bushes means the suspension works better and the bushes do not wear out. And they do come with stainless steel inserts if required!!
I don't know what the issue is to be honest Chaps; they don't sqeak, you get a race or road option ( normally), which depends on the shore rating ( something like that!) . Roll bars work better with them too - I found a company called jepe which offer the earlier front bushes for the 4200 Maserati with poly inserts; they certainly look like Granturismo front bushes - does anyone know if they are the same?
If a company did a set for the Granturismo I'd buy it; c'mon Conaero, you know you want to!!