Guys, thanks for the replies all of the comments have been helpful.
First off, no, I do not have a drawing, and that is something I am going to have to come up with.
Working with steel vs aluminum especially from a welding standpoint was a really helpful comment as well as the ones related to welding shops vs machine shops, so those are two aspects that I'm going to sort out and see which is best, etc.
Finally, the FSA might be a really helpful consideration. I was thinking of using my existing pier as a guide so that my rotating pier adapter would fit on properly, but, if I have the pier made with a flat top welded in place vs the machined ID for the RPA then I could just mount the FSA to the flat top and my RPA would fit on it with no worries.
So, several things to think about here.. but definitely thanks to everyone who responded.