"When the spring says,"good up to 500 lift" does that include using 'top hat' seals?"

No, the spring has no idea what seal you're using. All it knows it that with the spring at installed height (you have that figure from the mfg), you can compress the spring 0.500" from there before you start getting coil bind.

I assume you're talking about "umbrella" type seals that look like an upside down bucket that ride on the valve stem and fit down over the valve guide.

Beg, borrow or steal a set of snap gauges. With the head on the bench so that the valve will go into the guide sideways, slide in a valve and push a seal down on the stem and over the guide. Get some thick grease and apply liberally to a retainer and a set of keepers. Without the spring, assemble the retainer and keepers onto the valve stem with lots of grease to hold them together on there. Get a buddy to help you if necessary. With the valve on its seat, snap gauge the distance from where the spring will sit under the retainer to the spring seat in the head. Write down that distance. Now open the valve as far as it will go until the bottom of the retainer is against the seal. Don't force it. Now snap gauge that distance and write it down. Subtract the 2 numbers you wrote down and that is the valve lift you have to play with before you have seal interference.

P.S. forgot to say, you'll need a dial caliper to measure the distance on the snap gauges.