I have a 68 400 convert with the original 400 it came with from the factory and the phs says its a true 400 car. Date code on the block is L207. It appears to have never been removed from the car. The block has the partial vin that matches the cars vin and its not a restamp. The intake manifold is the correct casting with a date of L137. The heads are cast 15 on the center exhaust ports which from what i've researched are off a big car. The heads are date coded L067 and L197. Coincidence or could it have left the factory that way? I know the exhaust manifolds have been changed to 69 bird (casting 9796155 date J169 LH and 9796992 J258 if it matters)so the car has had a few changes but other than that its pretty much all original. Thoughts??