Buddy of mine blew a HG like that after running dozens of bottles of n2o threw his stock 100K+ mile 87 mustang with a 150 shot on it. It didnt get any antifreeze/oil mixing or at least did not get to that point. He drove it around for a good bit too and took it to the track and ran a friggan 13.9 or some BS. The times had us thinking the problem was elsewere since he had noticed some issues. cleaned up the block really well and had the heads milled and ran fine.
BTW this car was a FREAK....bone stock (bought it off his mother) it ran a 13.9 @ 100 with everything stock...air silencer, gears, timing, air filter...it even had a role of paper towels jammed up between the airfilter and air silencer. Beat the tar out of ALOT of cars it should not have.