Have you fitted the large valves yet?
Whoever you hire to do them would be able to also fit new guides, seats and stem seals ( complete rebuild)
I would also change the welsh plugs in the head too for if they leak later you’ll have to remove the head to replace them
Valve spring rate varies based on cam design, lift, duration, how high you plan to rev it, for a Volvo designed cam there’s no need to change springs. If going beyond Volvo cam types, stronger springs may be necessary
