I just looked over several engines I have apart on the bench. The seat width in OS engines appears to be ~.015", 0.4mm. A Magnum 91 RFS with loads on time on it was interesting. The valves are visibly worn, but the seats are like new. I noticed my low time Enya 46-4C had worn seats and guides. The Enya appears to have a multi angle seat, the only model engine that I've noticed it on. I don't have many Saitos, the FA-40 appears to have a wide seat, but the valves are relatively small. This FA-40 appears to have a damaged intake valve. There is a blemish on the sealing face. It's in pieces for repair now because it leaks. I'll probably regrind the valve face on the lathe. I have an OS FS-91 SII I picked up as parts with very wide seats. This engine looks like has loads of time on it. Over all I think seat width is intended to be what OS uses. I'll pull a new engine and have a look.