Are the jewel box engines the good ones

It's a stepped cylinder. That portends good things.

The Hopeful mark

Mark, the best way to check is dismantle the engine. Below is my jewel box TeeDee from '75 (see the Litho mark on the Instruction sheet) with stepped wall cylinder and its piston easily passing the TDC, meaning it is non taper...this is why I assume, taper bore may have discontinued earlier (around '74 I guess) than jewel box.



Mass produced, old-stock engines like Black Widow still had taper bore in 1973, like mine, which is a first production run BW, with the red rubber spinner and stepped wall cylinder. (BW production started in 1973.) Later produced production engines and high end TeeDees had no taper bore, I guess.

Venom and Killer Bees in short production run also reverted to taper bore, as a means of making them more attractive in years when business began to decline, but their production numbers may have been much smaller than TeeDee-s.

So I guess if there is a Litho mark on your instruction sheet from no later than 73-74, chances for taper bore are good. But removing the cylinder and pushing the piston up by hand will tell you the truth.