I attempted to put on new rocker arms on the intakes valves last night and everything looked great except I had a pushrod touching the bottom of a guide plate at max lift.

If I take the guide plates off and grind off some of the bottom [__] does it matter if I grind to much off? Are the pushrods held in place by touching the sides of the guide plates? I hope this makes sense

I am doing this while the boat is on the lift. I cant take the guide plate off grind off a little and put it back on and so on.

You're talking about making the slot longer.. I believe.... I have done this without problems, but of course it all depends on how much you need to take off. The guide plate holds the push rod from swinging side to side so the rocker doesnt fall off the valve tip.. Off course if you remove too much then it can weaken the piece... Good luck with it..

Yes I need to make the slot longer.

What I was trying to ask if I only need to take off .010 thousands to get the need clearence, but I take off .030 would that be a problem.
Not to hard with a grinder and air