I would be highly suspect of any claims of any ride termed "mega-bell" prior to the 80's for sure. I want to say that the Zildjian Earth Ride had a prominent sounding bell back then. It was a heavy ride with an unlathed topside. Any pressed cymbal will have to be on the heavier side to produce a prominent bell sound. A true rotocast cymbal holds the possibility of having a bell that is much thicker than the bow of the cymbal. In fact, I have a set of Zanki rotocasting hi hats from the late 70's or 80's that has a bell that is thicker than many 21" ride cymbals.

I know that the Zildjian Z line produced a ride that was named "mega-bell."

What is the end result of your search?

The Sound Creation Bell Ride was manufactured by Paiste and was available pre-1980. I used to have one (a 20" model) that I traded for some hats that I like. Was it the first oversized bell on a ride cymbal? I'm not sure. It's the first one that I saw back then.

The word "Mega" is a recent addition to these types of cymbals by several manufacturers, because "Bell Ride" apparently isn't, well..."mega" enough.

I forget what these were called originally, but I often see them referred to as "mega-bell" rides. I believe these came around in the '60s.

http://www.ebay.com/itm/18-Avedis-Zildjian-Cow-Bell-Crash-Ride-Cymbal-1800g-mega-60s-vintage-RARE-/331054851724?pt=Vintgae_Drums_Percussion&hash=item4d1468268c

Interesting. Even in creating a larger than normal bell, that thing is huge! Do you think it was originally an 18", or a larger cymbal that's been cut down?

May I mention this old thread?

http://vintagedrumforum.com/showthread.php?t=31931&page=2