Bronze has a higher coefficient of thermal expansion. Run tighter clearances and you stand a good chance of seizing a valve. This is especially true with iron heads. I've seen that play out a few times at the track.
To the op, guide clearance depends on a lot of things, partly on valve seat contact width (how hot the valve gets), material of the valve, use (running WOT for miles at a time like land speed racing is going to make for a hotter valve), and material of the guide.
Your best best if you contact Chris @ Schumann is to let him do it. He knows where clearances should be for his stuff. Edit: It also looks like he has a Serdi and does valve work. Honestly, I would just send him the head tell him you want his valves, liners, and a valve job, and be done with it.
Note exactly sure what the motors want on angles. Probably go with a full radius with a 45* seat on the exhaust (no back cut! you don't want to promote better flow in the opposite direction). A a 3-5 angle on the intake valve, with a back cut. Go with a 45* seat on a street bike, 50* seat on a race set-up.
edit: I see you're in Australia. I guess your best bet is to call him up, ask where things need to be and have a local component machinist do the work. Lots of race engines being built there, so there are some great performance machinists around.
