It is essential to lap the valves - they may have been leaking, and most likely they have not been lapped in the time it took to wear out the rings, so it is more than due. The process is usually simple, but that depends on the condition the seats are in at present. The first thing you need to do, though, is check how well the valve stems fit in the guides. If they are rattly-loose, you can't lap the valves successfully until they are corrected. I suggest you follow this process. First, measure the valve stem diameters, in the wear area (i.e. where they slide through the guides). Nominal diameter is 0.217", minimum is 0.209" for inlet, 0.208" for exhaust. Second, try to measure the amount of slack between stem and guide. I would do this with a dial gauge against the valve head, pushing it from one extreme to the other and noting the movement in between. I think you will need to set up a stationary object close to the valve head, then use feeler gauges. The nominal valve guide internal diameter is 0.217", and the maximum is 0.222". This means the maximum valve head movement (worn out valve stem in worn out guide) is 0.011" inlet, 0.012" exhaust. If you have more movement than that, you can calculate what the movement would be with new valves in the old guides. If it is still excessive, you need to either ream out the guides and fit new valves with oversize stems, or renew the valve guides.
Please let us know how the valves and guides measure up. There is no point in lapping valves that you are going to have to replace.
