Well it _appears_ this issue is due to the client's PO Entry files being rather large. Header has 15,150 records and Detail has 83,908 records. # of days to retain completed PO's is set to 360, and they look to be performing P/O Period-end Processing in a somewhat timely manner. In general they apparently issue lots and lots of PO's.
Ran the data conversion without enabling PO History Creation.
Looked in Sage 100 and saw that the new PO Hist Inq has 0 records (as expected).
Ran the PO History Creation utility (only took 3min!!) ""This utility will create records in the PO History files from standard orders, drop ship orders, and material requisitions contained in the PO Data Entry files"".
The new PO Hist Inq now has the 15,150 PO's.
I don't understand why we ran into this issue if after-the-fact it only took 3min to create the PO History. I also don't understand why the data conv appeared to hang on ""A/P Creating new tables"".
Btw, before data conv I had also tried rebuilding Keys and Sorts (po, im, ap, ci) but that didn't seem to help.