This is an idea of what I have come up with so far, comon, lets fix it! What I did here was:
-snip-
SELECT WORKPO
COPY TO temp FOR po = varpo
USE temp IN 0
SELECT temp
COUNT TO ct
-snip-
-keep in mind that WORKPO and HISTPO have the field "PO" indexed-

wait window 'TEMP has more 1 records'
SELECT histpo
SEEK varpo
IF FOUND()
COUNT FOR po = varpo
IF _tally = ct
SELECT temp
SEEK varpo
SELECT histpo
SEEK varpo
FOR i = 1 TO _tally
IF class = varclass AND ;
fund = varfund AND ;
udds = varudds AND ;
amount = varamount AND ;
fy = varfy AND ;
activity = varactivity AND ;
account = varaccount
SELECT temp
DELETE
ELSE

ENDIF
ENDFOR

ELSE

ENDIF
ELSE
*APPEND to HISTPO
SELECT workpo
REPLACE which WITH '3'
ENDIF