I'm in the same boat.
Fresh rebuild 261 - driven less than 500 mls (without any problems) - than sat for over 10 years, now it's not firing on cylinder 2 and 3 - tons of gas in the oil.
Checked all the usual suspects from stem seals, valves, pushrods, electrical, carb etc. - no dice yet.
First (dry) compression test was fine, gonna do a wet one next, and also a leak down test.
Can't think of much, which caused that on a perfectly fine engine, just by sitting several years.
