Welcome to the shop, Mike. There are lifts with aluminum plates - JessEm Mast-R-Lift II is an example. I have one and love it. Unfortunately, it's pretty pricey. Double unfortunately, I don't think your PC690 is adjustable from below (above, when mounted in an RT) so it would work ok with the aluminum plate but height adjustment is going to be harder. I agree with bob, AL is a better material for this application.
By the way, it would be good if you could fill out your profile a bit more. Folks here like to know who they are talking to.
Measure twice, cut once and CROSS OUT THE WRONG MARKS.