Small block MP .528 solid cam - which valve springs?

Not sure how thick - do you mean how tall? If I use hughues viton seals, they are 5/16' X .530'. Pic in their tech article shows measurement from the top of the seal to the bottom of the retainer.

.500 lift includes subtraction of lash? Cam is .528.... what do you set your lash at?

.530 is what the guide was turned down to so the seal would fit.
But if that clearance is with the seal included, cool.

I've set it tight, I've set it loose.....I most power is had with the factory recommended .028 int /.032 exh - thats where I run'em at.