Valve seals tore on break in

Having to cut the guides. It's not necessary on everything, but you need to CHECK on everything.
I suppose that's true. I work at a machine shop, so I do it anyway. Old cast iron heads weren't machined close most of the time so I like to set everything where it is equal & usually cut .100 off the top of the shortest , then match the rest. I also cut the guides od to .502 on all cast iron heads. The new guides I install are that size. I also check what cam lift is just so the clearance is there.