[david c.]

easiest is to check the VIN, as the other posters have mentioned. if it starts "912..." that's a pretty darn good indication. Also, there is a wierd ingot under the suspension of a 912E, presumably (?) to cancel out some harshness of the four-banger. It may have been removed for the six conversion. I don't think a regular rear sway bar will clear it either.

Check the gauges. A 912E has a 5500 or so redline , no oil pressure or temp gauge, etc. (although a decent swap for a six should have included the updates).

I don't believe any 912E's came with rear sway bars. I am not sure if all 76 911S models had a factory sway bar. I doubt it. The 912E has a tiny front sway bar, I think it's like 16mm. Mine is about to come off!

No oil cooler or plumbing originally in the front end. Of course, that was probably added during the conversion. An oil tank was a component of the 912e, it's not a dry sump engine, but a conversion would necessarily require this of course.

Rear brakes are distinct from a 76 911 also. I think the 912E was also equipped with steel wheels standard.

Also, there are transmission characteristics; like the ring and pinion are different.

David