Just in case you wind up with this question, The Viton rear seals have a big metal rod in them and are not made to be trimmed. I went through that on mine. Called the manufacturer about it. The seals are not sensitive to the amount of material removed in a line bore. They are made to be installed the way they are made.
If you do ..you use a belt sander. Paint pen mark it white just before the edge leaving black the amount you would remove. That's how I'd approach that venture.
Light amount of sealer on ends and all over the side wedge insert thingers. Lol
