UL pistons and valves

I am in the process of rebuilding a top end for a UL and have two questions. 1. both my cylinders have a hairline crack at the head steady headbolt on the gasket surface, you can barely see it, and one cylinder has a crack in the exhaust port just where the guide protrudes through the metal, do i need to get these welded or ?? the guide area crack looks like a problem. 2. what are the best quality aftermarket pistons and valves and guides i should be purchaseing to complete the rebuild.
Thanks.

The headbolt hole cracks won't be a bother. The crack at the guide hole won't give you any trouble, a .001-.0015 press fit in a clean true hole is important. The nitrided valves and cast iron guides guides available from Rowe are the best.