[Sorry, the below is a train-of-thought post that I'm keeping for my own reference... I think as I went, I found the answer... I hope. Still doesn't explain why this blasted Hughes flexplate doesn't fit on my converter!]
My engine ('74 318) has a cast crank. Does this make a difference (in the converter used)? I'm wondering if this converter isn't right for my cast crank application, or does it not matter? I'm hoping I don't have to buy a different converter. (at least now now, even though I know the stall isn't really high enough for my 284/484 cam, but I wanted to try it anyway since I have it). I don't see any extra weights on this converter, which is why I'm asking.
I think I have a stock converter in the closet, and there's a good chance it's for a cast crank... but it would be stock stall, which would be completely not ideal here.
And in any case, would that make a difference in how the the flexplate would fit?
This is getting pretty confusing and not as straightforward as I'd hoped... but then when is it ever!?!
EDIT: I found a post on moparts that I think explains it. It looks like I may need to get a flexplate with weights added to be able to use this neutral balance converter. I'm not sure it explains the bolt pattern fit issue, but either way, with a cast crank and neutral converter, it looks like that's what I need to use. Apparently B&M makes one, but I can't tell on their site, so I'll have to call them Monday. The Hughes flexplate isn't a total waste, because eventually I'll need it for one of these 340's I have, or for my GTS, so no big deal. I guess this is a good thing to have caught now before I got it running only to discover I have a vibration or break something.
But hey... that's the main reason I'm doing this project, to learn, and it's certainly a plan that's working!
EDIT #2: More research shows that ALL 318's should have a neutral balance converter AND neutral flexplate. So, what I have should work (if I could get it to bolt up). Apparently, the cast/forged crank issue is only for 340s, and of course 360s? Is it true that all 318's are internally balanced, and forged crank 340's are internally balanced, but cast crank 340's are externally balanced? That might make this whole thing make sense.
Hey at least with all this research by the time I figure all this out, I'll know a heck of a lot about converter/flexplate combos!
EDIT #3: Just found this on an old FABO posting, and I think it makes it all make sense. Apparently my converter and flexplate should both be neutral: "externally balanced engines (340 or 360 or 400 or 440 with cast cranks) use a engine specific balancer (360 is different from 340 is different from 400 is different from 440) and the flex plate OR torque converter will have an offset/weights (but not both of them)."
One of the main things that confused me here is that the B&M converter instructions talk about cast crank engines needing a balancing, and they have a chart showing 340, 360 and all the big block engines, but NO mention whatsoever of the 318. So, I referred to their cast-crank directives, but I don't think that applies to 318's since they're all internally balanced. No love for the 318 at all.