water in oil


Last winter my '89 Sportrak froze up due to insufficient antifreeze, doh! Sat around since then, just got around to fixing it... On inspection it looked like the head gasket, stripped down, no problems, but when I drained the sump I was suspicious at the amount of water that drained out. Far more than you would expect from a blown gasket or cracked block/head. Plus the amount of brown sludge that had to be cleared from around the water jacket.
However reassembled and decided to top up the water but left the sump plug out, once the rad had filled the water just poured out of the sump. Too much for a cracked block or anything like that.
Totally disheartened I packed up, but while clearing up I spotted a small core plug where the head had been laid, but don't remember seeing anywhere this may have come from in the head, but it is slightly distorted and small indents where it may have been lying in the head and when the engine was running the rockers have hit it....
SO, my question is: are there any core plugs in the head that would allow water into the lub system if missing?
can anyone help, because although old its very low mileage, but not worth spending a fortune on..