I think the standard ports on the 16V motor is quite good. It already has 45 deg seats I think and the shape of the ports look good, and the size is OK. Maybe you can do a radius cut on the valve seats, but is it worth the cost?
I don't know if you know about Glenwood Motors here is S.A.? (They built a 1982 GTV6 3.2L with twin turbos, 500 bhp +, I think Rare Motorsport in Britain has it now.) Anyway, they have apparently modified a few 155's. Only changed cams, ECU, exhaust and air filter, with good results.