Well, if ya cant find a plug try pulling out the bottom bolt on your cover. It should allow you to drain most of it out, and really if it's that old and nasty ya may wanna have a peek in there to see how much of it has turned to solid muck & needs to be scooped outta there anyway.

1956 GMC 370 dump " 'Tater "
1970 VW Volksrod "the Black Bomber"
2007 Chevy Avalanche
2020 Jeep Cherokee Trailhawk,
2005 Harley Davidson FLHTCUI

I dig all cars, old and new, whether they were hammered out of American iron, German steel, or Japanese tin cans. Being unable to appreciate them all is missing out on a world of great things.
But thats just MY opinion! :P