I know this may be silly, but I pulled the engine and see that the flex plate is weighted (external balance?) It is a 1976 350 Olds. My question is, Is there only one way that the bolts will line up? or how do I know it's mounted correctly?
The car came from a previous owner and I am discovering some questionable mechanic work is why I ask.
thanks

 

There is only one position in which all 6 bolts will line up.

 

Thanks, I knew that most External had dowels or pins just new to Olds, just making sure!

 

It's not a perfect hex pattern

If you measure hole to hole you will find there are Short, Medium, and Long spacings.

Pre-68, one hole was offset about 5 degrees or about 1/8" at the holes.

1968+, TWO holes were offset, the other way, about 5 degrees. Thus, the pattern for '67 is
MMMMSL or of course MMMMLS if you go the other way 'round
Four Mediums, one Long, one Short

The pattern for '68+ is
MMSLSL - two of each spacing.

Because of these variations, you cannot mingle nor install the flexplate incorrectly- with all the bolts.

I have however bought an engine with the '68 flexplate stuck on a '67 425 crank. Flexplate flipped over so that 5 of the 6 lined up... and 5 bolts installed. Balance weight nowhere near where it should be.

I just wanted the engine for parts anyhow.

 

thanks for the explanation!

 

Nice explaination, however just to clarify the OP asked about Olds 350s, there were no pre-'68 350s, thatt was the first year.

 

The reality is that there are only two types of Olds flexplates, 64-67 and 68-90. Engine size doesn't matter. All 68-90 RWD flexplates interchange. I've never seen one, but apparently the flexplates on FWD 307s with the 325-4L trans are smaller in diameter than the RWD or earlier Toro flexplates.