Why are you buying a new head if only the valves may be bent?
First order of business is to remove the head, remove and label the valves (#1 intake, #1 exhaust and so on). Then test and measure them to determine if this is the actual problem. If so, you now have choices: replace only the bent valves, replace all valves, or replace the valves and have a bit of machine work done.
If the latter is your choice, just make sure you take precautions with reassembly and you'll be fine. By the way, are you following the manual for torque sequences to install AND remove the head? It does matter for removal too...