I was going to buy a set of 113 heads which I was told would handle .525 lift, well after some double checking by the seller he told me the valve guides were milled down but with the current valve stem seals it still is only .470 lift. He pulled the seal and it is .800 lift to the guide it self. Is there a special seal that needs to be bought when the guides are milled down to accept the higher lift? I need .525 lift with my cam.

 

Positive type viton seals are usually 0.150" thick, so that's how much lift capacity they take away.
Normally the guide tops and guide bosses (if applicable) both get machined to accept a smaller diameter, but normal sized seal.

A stock guide top is 0.558" - 0.560"
They generally require a seal diameter of about 0.530" so they will fit tight on the guide.

When they are machined down they are often trimmed to 0.500" diameter, and the guide boss is sometimes trimmed down as well so a normal height seal will still fit on the guide. A 0.500" guide would need something like a 0.475" seal I.D.

The machining operation should have taken care of the spacing, but yes the new size seals often have to be used.
You may also be able to gain clearance for more lift by using spring retainers from a chevy 4.3 liter vortec V6. They usually add 0.086" - 0.094" of travel over stock L98 retainers.

If you need to get new seals they usually cost under $20 for a set of 16. SBI has a large selection to choose just the right size to fit what you've got. They list all the dimensions of the seal.
http://www.sbintl.com/valvestemseals.html

Go to downloads and look through the catalog listing.

 

He said that it had umbrella seals on it now, Which I dont understand why they wouldnt allow the full lift, and the guides dont look to have enough meat left on them to support a positive stem seal. He said his buddy was running a high lift cam but something doest sound right to me. Umbrellas should allow full lift right?

 

Umbrella seals are usually around 0.120" thick, so provide more clearance than positive type seals. I'm thinking a picture of all this would help.

There are positive seals made for 0.500" guides. If the guides are thinner than that then they must have been trimmed by hand tools. - that's not normal.

 

its not the thicknessits the retainer to seal clearance Im worried about, hes supposed to send me a pick of the guide tonight. Ill post it when I get it