Chrysler 6 banger flatty

HI, I've always thought flatheads were pretty sweet. Anyways Ive got an old '49 Fargo 1/2 ton, (its just a dodge that was made in Canada i guess). Its got what I believe to be a 218cu in 6 banger flatty in it and its seized. The trucks been parked outside with the hood off for probably many years like 20 or 30 (it was a project that was started by my uncle but it never took off). I don't know if the engine ran when he parked it or not. I've dumped a lot of WD40 down the spark plug holes and It hasnt done anything yet, (Its been months since I've done it). Should I do it again or just give up on it. Someday the truck is getting a 318 polyhemi but I wanted to see if I could get the 6 to work and driver' around for kicks.

I also got 2 other 238 Chrysler industrial flat heads (they look identical to the 218) there in old combines in the junkyard though (they might just run infact with less messing around then the 218). And I have a factory replacement 1948 Flathead v8 ford, thats also been sitting out in the open, with no plugs in it, would it be worth my time to be fixin that thing up for something?

Diesel fuel, for some reason, seems to work good for breaking them loose, too. Don' t know why. Buddy of mine told me to try it on a 410 Merc motor that I found. Got it loose.