The tank on that bike is from a Rupp. I would guess the original was the ARCO tank. Similar in design but it's stepped on the top
Don't get me wrong. It's a nice example of a Murray, but these were sold nationwide at Walmart and other retail stores. They were mass produced. They will most likely never be rare in the sense of other bikes, and they don't have the appeal of older generations of bikes.
I had one with an engine built the last week of December. I have doubts it would have made it to the showroom floor and into a home before the end of the year, but it was still a 68 model.
So are you asking if there are two-piece engine plate TT500 models out there? Rupp would have retooled...