If the head has any amount of miles, it will have shagged guides, as well as a few valves too.
Just as example mine needed 16 new guides, and 8 new exhaust valves, not bent or leaking, but thinner edges than I would accept, so binned them.
All in with complete overhaul plus 8 VAUXHALL exhaust valves machined to fit it came out at about £500.
Added a group a gasket, few cometic gaskets from Matt L(01543 484488) all was well.
Cossies suffer terribly from guide wear.
I would be tempted to clean out the tappets first, as they are easily cleaned, often just gunge/crap stopping the ball on the seat holding pressure.
tabetha