I'm in process to get cylinder heads rebuild, what is current consensus what parts should be replaced for proper job and what can be re-used if condition permits? (I have to order parts for machine shop)

- guides and stem seals will be replaced anyway (when rebuilding, can std size quides be used or do they need to be oversize?)
- intake valves ok to re-use (if straight and enough material left)?
- Exhaust valves should be replaced?
- how about valve springs, re-use or replace?

Other suggestions what to replace/re-use?

This will be for stock 2.0 (130hp) alu engine.

Many thanks!