Thanks @WayneSchulz -
Also I'm done with this for now. I ended up testing on a much faster computer and got it to renumber at 13 customers/hr (from 7/hr). Also find several files that had no index at all involving ARDivisionNo and CustomerNo (e.g. SO_LotSerialHistory) and after taking care of that, I'm at 16 customers/hr. Converted that data to SQL 4.50 and it's 15 customers/hr . Statistically the speed improved over 100% but still way too impractical to do a project involving thousands of customers with real client data. Some type of Set processing is necessary to take this to another level.
@DawnAnastasi - in version 3.74 SQL, specifically 3.74, they did make stored procedures for certain portions of AR customer DRM and AP vendor DRM. For A/R the proc was only for where DivisionNo + CustomerNo in an index like SOE, ARV, PO1, POP, etc. (which coincidentally are part of indexes in 4.5 either). For A/P, it was GL_20 and JC3. There were also a special T/C Period End proc created as well.