There was nothing mentioned to indicate that this engine was anything other than a more or less stock engine. Stock, it will have 28 oz in external balance. Changing to internal balance would be quite an unusual (and expensive) alteration for a run of the mill rebuild, but I guess we can't rule it out.
By the same token, we can't rule out that the engine has a special offset ground stroker crankshaft, custom length con rods etc.
But all are highly unlikely.
He didn't even say that it was rebuilt.

 

This is a stock '68 302. I bought a long block replacement so it may have oversized pistons but it's not a stroker motor. I went ahead and ordered a 28oz flywheel with new PP and clutch disc to just replace it all at once. I'll let you know how it goes once I get it installed, but I sure hope this makes it idle smoothly and eliminate that 'shake'. It was never violent and didn't feel like a misfire throughout the rpm range, I seemed to feel it most at initial throttle, Again, I assumed some of this was just being an old truck but I'm counting on this to make things better. Appreciate everyone's feedback.....

 

That sounds good. I guess we should double check the balancer on the engine as well, in the remote chance a wrong balance one was put on. What are the casting numbers on it?
Is there an obvious counterweight on it?

 

You should also make sure your harmonic damper/balancer matches as well. That ad the flywheel go together.

 

Beanscoot, the harmonic damper is obviously weighted but I can't easily see the casting number now. This weekend I removed the trans and installed a new 28oz flywheel and new PP/clutch kit. I couldn't quite get the trans stabbed by myself, so I have to wait until this weekend for a buddy to come help get it in. I think the shaft is touching the pilot bushing, it's that close to going in. Anyway, I'll let you know how it works....

 

If there's a balance weight in the damper that means it isn't the six cylinder unit, so that's good.
Here's the 28.2 and 50 oz-in dampers:
Edit: Strangely, the caption incorrectly states that they don't balance anything.

 

It is a harmonic damper with counter weights for external balancing.
We just get lazy and call it a harmonic balancer.

 

So I was able to find my notes on the original harmonic damper. It was D20E6316-A2A. I know for a fact it came off of a 1973 Gran Torino 302-2V. What I "believe" is that it is a 28oz imbalance. The replacement I used looked exactly like it, so I assume it's the same imbalance. The application said it fit 72-74 Gran Torino and a whole host of 1972 to 1980 model vehicles. If so, the new flywheel should work....I think.

 

Maybe..!?!?

 

I should have used "hope" and "surmise" a few times as well. We'll know this weekend after I get it stabbed and fired back up. Maybe....

 

Referring to the images of the balancers I recently posted, it's quite easy to tell if you have the 28 vs. the 50 ounce version.

 

I got the transmission stabbed today and started it up, happy to say that it has lost that shake and has a smooth idle. Only vibration is what you would feel thru the rubber motor mounts, so I am very pleased! Thanks to all who contributed here, I'm very pleased.

Beanscoot - This is a pic of a damper like mine but not the actual one. Mine came off a stock 1973 Torino 302-2V.

 

Hmmm, that one doesn't look like either one I posted, so I guess it's not so easy to tell!
Anyway, a '73 Torino 302 would have the 28 oz harmonic balancer, so you no doubt have the right one, confirmed with the smooth running.
Good work!