Busy spell, I didn't get to everything on the to-do list, but a good breakpoint for an update.
I noticed that for 64-bit static LIB files with a CONST section, for now, the source file will require a CONST section in order to work properly (otherwise the LIB CONST data ends up in the .pdata or .xdata section).
Also, the PINSRB PINSRD PEXTRD instructions shouldn't assemble with a 64-bit register, but they do, still looking into that...