My technique...
Sean-
I've broken six engines like this free in the last three years. MY technique evolved from the soaking/grease injector techniques after having more success...
Pull the head, get a couple'a drill-wheel brush... a plastic brush with light abrasive seems to do best, and an extension-rod to fit in in your drill. Don't use wire- it'll get snagged at the piston-bore interface point. Take that brush, and spin the brush up and down the walls with a cordless drill 'till the bores look clean enough to pass. Use a wet-dry vac to suck out all the crud. Clean up the valves, put a sucker-stick and some compound to 'em, lap 'em down 'till they make a nice seal pattern. Remove the tappets, so the valves will all stay sealed shut. Get the gasket good and clean, put a light film of grease on it, oil the bolts, and put it back into place with proper torque. (Be careful when cleaning the carbon deposits off... especially if you find white- it's lead, so don't breathe it!).
Smash the sparkplugs... knock out all the ceramic, but keep the sleeve. Weld a short piece of 1/4" pipe to each one, thread 'em into each hole, snug 'em a bit.
Mix up even quantities of diesel, ATF, and Acetone. Fill each cylinder... to the top.
Make a 7-way manifold... hook up flexible hoses and couplers from the manifold to each plug pipe. Hook a hose with regulator to the last manifold fitting, dial up about 30psi, and walk away for a week.
When you come back, pull the dipstick. Sniff for acetone... if so, that means it's getting pushed through. Relieve pressure from hose (wear goggles, in case it spits at you!), refill cylinders, set regulator to 15psi, and walk away for a week.
Eventually, all cylinders will flow this witch-brew.
Next... re-plumb the oil-pressure gauge/switch port to a hose into which you can pump oil. Drain the crud out'a the oilpan, leave the plug out. Put a 5-gallon bucket under the oilpan, get or make an oil-pump that'll generate about 20psi, and feed it INTO the gallery. If the distributor shaft gear also spins the oil pump, figure out a way to keep the pump from spinning. Let the pump run for an hour or two... a day... or two... expect the bucket to look pretty murky after a while. When you're ready to give it a try, put a socket on the crank and see if it'll turn. I can't say wether mine was luck, science, or good technique, but my '48 Allis Chalmers sat in a field with no lid on the stack long enough to fill with water, and was stuck-rusted-tight when I got it... took me about 20 hours' labor to break it free, and it runs. Yeah, rings are all stuck, bearings are worn, and it definately passes oil, but it won't require a hammer to disassemble when the rebuild kit arrives.