flywheel (not flexplate) ID?

carnuck wrote: There was a difference between the harmonic balancers (3 bolt and 4 bolt) but I'm pretty sure the weight offset was the same for all years. There is a slight difference between the outer diameter of the 2 crank flanges so that one won't fit the other (can't remember which way). If you DO manage to get the wrong one bolted up, this may happen.

   not always. You can still have the correct flywheel and still have it explode.
Ive seen one 401 flywheel explode, and it wasnt pretty.

carnuck wrote: Far more likely with the wrong flywheel though (the reason for scattershields)

.and the reason I run one...:

but,back to the original problem?

tomslik wrote: carnuck wrote: Far more likely with the wrong flywheel though (the reason for scattershields) .and the reason I run one...: but,back to the original problem?

   yeah. Go back to the original problem.   I sure agree with that. I dont understand what other things have to do with the OPs question.

I got this info years ago when I put my 401 together. Mind you I put the 319 6929 on the 74 401 and had it externally balanced. It was not off by much and it did bolt directly to the flange of the crank. The bigger balancing issue I found when I rebuilt the motor was there were two different number connecting rods in the motor and they weighed 70g different from the rest so I had to get replacements for them.
Info:
66-69 290 317 9069
70-71 304 319 6927
72-79 304 321 2651
67-69 343 318 1609
70-71 360 319 6929
72-74 360 321 2653
68-69 390 319 1662
70    390 319 6929
71    401 321 0496
72-74 401 321 2655
Hope this helps.

a little more info on this car, it was bought this way 304 balancer,360 flywheel, 401 block. is it possible it has a 304/360 crank?
owner says it's a dog....
my suggestion to him was remove engine and look-see....who knows whats been thrown in it for parts.
it DOES have the correct (for a 401) flywheel and a new aftermarket balancer with supposedly the correct weight on it, still shakes bad.