I have a 68 383 Dart GTS convertible. The assembly date on the original engine is 9/20. The engine has 516 heads on it, not 906 heads as I would expect. I know the 67 383 engines in Darts used the 516 heads. The engine has been rebuilt at some time in it's life. Is it possible that these heads are original to this engine, and were left over parts that were put on from the factory? Anyone seen this before? Also the numbers matching block is not stamped HP, nor is the block in my 67 GTS Dart (assumed to be original - cast and build dates are just prior to vehicle assembly date). Anyone seen this before?

I have heard of another '68 383 Hardtop that was not stamped HP. 906 heads, if I recall.

Is your car an auto or stick? I have an auto. Non matching block

Dont get to talk to many '68 383 'vert owners.

It's an automatic. My 67 GTS 383 convertible is a 4 speed. I also have a twin to my 68 car - a 68 340 GTS automatic convertible. Both 68's are red with black console interiors.

For what its worth I owned a 68 Dart GTS 383 4 speed Convertible. When I purchashed it in 1974 it was dead stock with the exception of a Hurst shifter(Inland shifter in the hurst box in the trunk). As a 21 year old punk I hot rodded it in 1976. I was going to install a "built" 440 I had. Stock pistons,.030/.030 crank stock heads and a Gratiot Auto Supply 270/470 cam. Anyway a local stock car racer doing the machine work said the heads were junk. I knew the 383 heads would fit so I tore the motor down. The heads were 906. Last I saw of the car my buddy sold it to someone in Ann Arbor Mi around 1978. The short block could still be sitting in a barn in Reeedsbug Wi. Who Knows? Learned a lot about motors since then. I should have left it stock and kept it. The next car I bought was a Volare Road Runner. Believe it or not I still own it.
Doug
Doug

On the 68-68 383 4bbl motors the blueprint specs were a +.020 on the piston deck height. If you run the steel shim headgasket you have a real good chance of having piston to head contact.
Many years ago I picked up a 68 ChargerR/T for parts. It had the same situation, when I tore the motor down I found some clown had installed 516's. The pistons had been kissing the heads. Dave

I would suspect they are not original, but there were weird things done form time to time. Where are you located? I know there are a few 68 GTS convertibles around, but most of them seem to stay in hiding (like mine that needs a restoration).