Assessing the condition of the valves, stems and guides is part of the diagnostic that the machinist should do. I would suggest having your rebuilder tear them down and note any concerns before you start porting. If he is good, he will even point you in the right direction on your DIY project. After you finish, he can put them back together with the notes made at disassembly.
If you plan larger valves, and expect to replace all the guides, it won't matter at all, but there still may be warning signs worth noting at disassembly.