[jeffspower]

I don't think any of the 235's had a threaded hole- just a dimple in the center of the crank. The '58 235 I rebuilt a few years ago didn't. I tried drilling a hole, but the crank was HARD steel. The angle of the dimple & the drill bits I had were different enough it would knock the cutting edges of the bits right off. And I had the engine on a stand out in the open. I think it is something that would have to be done on a lathe with an endmill or something.

WD-40 isn't good for much IMO. I'd try PB blaster or Gibb's. You should be able to take the flyheel cover off & work it from there. I had an old V8 Ford flathead that went thru a flood & then sat a year or better before messing with it. We pulled it around on concrete dumping the clutch and it wouldn't budge- just drag the tires. I screwed the plugs out, sprayed in some good stuff, waited a month or so & it cranked over with the starter.