This is it - flathead goo. Grandpa's 8RT may have been a little extra blessed by its years outdoors, but you can generally bet that every flathead has some pretty foul stuff in its pan, lifter valley, crankshaft, and any other nook or cranny where stuff can settle out of the oil.
The shape of the pan was a bit of a surprise to me since I expected to see a flat bottom with the famous truck pan clean out. Apparently, in '52 and '53 they didn't have them. Another style of rear sump pan is found on Mercurys. The Merc pan sump is shorter, but deeper. Ford passenger car pans from '49-'53 (or '54 in Canada) have center sumps. I suspect they all hold the same amount of oil.
The back end of the pan showing the lower half of the rope seal partially pulled out to help you see it, and the bulge on the picture's right, engine's left, is for the oil pump.
The front of the pan with the rope seal still in place. The baffle on the right help keeps oil from being blown out the road draft tube.