Advice needed. flushing engine during intakee manifold gasket replacement

My wife calls me at work last week to say her car (96 Grand Prix) didn't want to to start. When it did she drove across town (about 5 miles). The temperature hand went up pretty high. Not into the red but close. I went down and popped the hood to find almost no water in the radiator. When I added fluid, there was a distinct "sucking" sound from the radiator. I pulled the dipstick and found lots of water in the oil. The engine would start but ran rough. I immediatley thought head gasket. But, there was no white smoke or steam. The guy that hauled it home for me said probably the intake manifold gasket. And after searching and finding this forum, That seems to be a trend with the 3.1L. I have disassembled the top half of the engine (boy that's fun) to replace those gaskets. My real question is, is there a good way to flush all the goop out of this motor while I have the top off? I was thinking of draining what is in it now. Then replace the plug and fill it up with kerosene to evaporate some of the water and wash the internals. Are there concerns about kerosene damaging internal components. Or is there a better way? Maybe just gas?

Any advice would be greatly appreciated.