From memory, the valve angles are supposed to be 1/2 degree interference, but when I machine them I use equal angles and do a light lap to finish them off. The exhuast valves on the B230FT are stellite induction hardened, and Volvo says that they must not be machined (ground) in order to retain the full depth of the hardening. I have known other rebuilders to machine them and they have not experienced any problems. However, I have never seen them warp or become ridged, so I simply lap them onto re-cut seats. This works just fine. The intakes can be machined normally. Keep the seat width to something under 2mm (.080 inch) using three angles, and that's it.
To save on shims, I reinstall the buckets in the original postions, with the cam in place, and then slide the valve into position and measure the clearance (no springs installed) I then grind the valve stem the appropriate amount to achieve the clearance. Volvo allows up to .5 millimeter or about .020 inch to be removed from the stem tip, and has a mandrel which is used to ensure that the valve protrusion remains within the adjustment range provided by the shims. I use that feature to set the clearances and avoid buying shims, which lets me use the original shim against the original cam lobe. Normally only about .005 - .010 inch needs to be removed, unless a seat has recessed, in which case buy a thinner shim.
The turbo engines tend to bell mouth the exhaust guides - not always, but when they do wear the amount is incredible. Fortunately new guides are cheap and easy to install. As there are no oil seals on the exhuast guides, the clearances must be kept tight to prevent oil burning.