overheated 5cyl, now oil pressure problem, ?

[Derek L]

Heya everyone, been a while since I posted.  I've got a 1982 coupe with the
2.1L WE engine and some oil pressure issues.  The previous owner overheated
it (I don't know how badly), had the head resurfaced, changed the head
gasket, then couldn't get it to run.  The P.O. is a VW enthusiast so I
figured he could install a head properly but probably didn't know how to
time an Audi I5 correctly or something easy like that.  I buy the car and
after much fooling around I get it to run but it won't make much oil
pressure.   When starting from cold it produces about 75 psi on my
mechanical guage but drops to less than 15 psi after a minute or so of
running.  It drops rapidly too, like from 75 to 15 in just a few seconds as
if something opened up after reaching a certain temperature.  I replaced the
oil pump today, cleaned out the pickup screen, installed a Mahle filter, put
in some 20-50 oil, and got the same results.  Good pressure for about a
minute then an abrupt drop to almost nothing.  Revving the engine will not
significantly increase pressure once it has dropped, maby a few psi, but not
much.  Also, if I pull the dipstick the oil looks frothy, with lots of small
bubbles as if it were carbonated.  Would I be correct to think the block is
cracked internally and dumping oil back into the sump after it warms a
little?  There is no oil in the coolant.  Anyone want a cheap coupe?

Thanks.
-Derek L.
Seattle, wa.