I wouldn't pay £300 unless you collect vintage Versace: the rayon blend is not a good sign.
I'd say the canvas is fused and the rayon is silk on the cheap. Italian fabrics have legendary thinness. The rayon will hold the shape of the suit, e.g. trousers (pants) will not go baggy readily: so yes its cheating but it will probably work. HOWEVER, Italian suits are thin to make them more breathable in the summer, the rayon will reduce the breathability.
IMO the key general question is whether it fits and (possibly) slim fits. A good fit is worth a lot of money otherwise spent on a tailor.
I prefer a medium weight suit and a good tailor BUT a professional full-scale jacket reconstruction at standard prices can be >£300.
My advice in this case is find a glove that fits and wear it: but its vital to accurately assess the fit, so e.g. get a friend who has experience and be very picky with slight pulls or bagginess and ignore shop assistants who say 'its great buy it!'.
1.This suit is too much for a 'vintage' wool-rayon blend.
2. A good fit and minor alterations, so try carefully before you buy.