[W126 Coupe] Very low oil Pressure :(

[Pavel]

Hi Guys,

Got my 87 560 sel running almost perfect after a head job(has slight
misfire due to bad spark plug wire).  Drove the car around on the freeway
for about 90 miles.  No signs of overheating or anything and no smoke. 
When I got of the freeway the oil pressure gage went almost completely to 0
actually about to between .5 and .2.  The engine was not ticking or
anything, when I put it into park it went up to 1.  Stays at 2 when driving
at 40mph anything over 40 pegs it out at 3. Pegs out at idle when engine is
cold. Never used get under 2 before the head job.  Idle is right at about
650 rmp.  I don't see how putting new heads on would effect the oil
pressure.  What would cause this?  How to fix it?  I put fresh 10 40 oil
into the car because old oil was deluted by gas (had a bad fuel
distributor) but I did not change the filter.  Any suggestions?
thanks
Pavel
380sec AMG
560sel
300cd