My guess is the valve stem seals you mentioned will last about 10,000 miles. Or maybe 8,000. Many, many people have investigated the valve stem seals. My recommendation is don't consider other than Volvo brand valve stem seals for even a second. The set for a white block is about $80 shipped to your...

This is a wetransfer link to TP-31714-2.pdf: https://we.tl/t-xNF3gMUJfM
It is valid unit september 19th.

Good luck and do not overtorque the headbolts as these blocks tend to crack after a head gasket replacement.

Piet