Heads off, stripped, light valve spring fitup on two valves, check for retainer to guide clearance at max valve lift to suit current camshaft, machine top of valve guides for positive viton seals that still allow adequate retainer clearance, machine valve guides for bronze guide liners, recut valve seats concentric to new guides, inspect valves for continued service, clean or replace as necessary, resurface heads, clean, reassemble heads.
I like to seal the valve locks in the retainers after assembly, prevents
oil running down the stem, they only need the odd splash, if running a bronze guide liner.
Cast iron guides do not survive with reduced lubrication.
Gary