I would love to know if there's a way to check my guides with the heads still on....springs off. When I changed my seals, I sure didn't notice any "wiggle" in the valves, but then I wasn't really looking for it.
Keep the piston near TDC so the valves don't fall too far into the cylinder, put a dial indicator (with magnetic base (mount it to the head or block)) on the valve stem and wiggle it to get a reading. There's a clearance spec on valve guides. Based on your valve stem distance (where you're measuring) from the guide, use geometry to figure the actual clearance. I don't have the specs at hand, they're packed in a box somewhere (I'm moving : )). It's in the service manual though if you can get your hands on one.