since you have the outboard turning stand, why raise the lathe?
Sometimes its just better to use the tailstock on the big stuff.
Here is the website of a guy that built his own riser for an older
Powermatic lathe.
http://www.billswoodcreations.com/turn-lathe-2.html
This page shows the design of such a riser block and the matching
tailstock riser.
http://www.thecooltool.com/files/dateien_222.pdf
If you did a more extensive internet search you might find a riser
block set for sale or maybe someone that will build you one.
Ted J
thelatentlog.com