'67 427 Exhaust Man. Bolts... Again

[Owen L.]

I am attempting to return my '67 L36's exhaust manifold attachments to a factory appearance. None of the bolts I have are GM so have nothing to go on. I know the JG says bolts, spacers, french locks along with a comment that there may have been locking thread bolts, no locks or spacers but none yet seen on original cars.

My engine was assembled mid-April '67 for my May '67 car. I really don't want to perpetuate the notion that french locks were original if there exists a solid possibility of locking thread bolts. I came across a number of threads year over year where Joe Lucia seems to be the only voice on this topic (quote below).

I do have extra original manifold bolts from my '72 LS-5. Would these be appropriate for use on my '67 if I do buck the French lock route?

I'm curious as to what folks have found on original 1967 427's as far as the exhaust manifold bolts are concerned. I believe the use of the "locking thread" bolts, GM #3909821, began sometime during the 1967 model year, if not from the outset of the model year. French locks were not used with these "locking bolts". It's going to take known original cars to determine this with any hope of accuracy because I believe that many cars have been retrofitted with french locks and, possibly, standard bolts in order to make them "correct". Even if the french locks have been added, the original "locking bolts" might remain.

One way to check for the bolts without removing them is to just check for their flanged head configuration. Most of the exhaust manifold bolts are trimmed (non-indented) non-flanged hex head. The "locking thread" bolts were used only at the end positions on either side.

Why do I think the "locking thread" bolts were used for 1967?

1) GM says they were;

2) The part number is consistent with a part number that would have been released for the 1967 model year.

So, why so many 1967 cars with french locks? Well, french locks are "one of these things that everyone wants to think their car came with". So, after all these years of Corvette restoration, they may have created their own reality.

[Stephen L.]

My '67 427/390 engine was assembled very late in March '67.
I believe the engine had not been "molested" by the time I purchased the car in 1982.
My engine has french locks and flat head bolts along with a washer between the manifold and the french lock.