I suspect, but don't know for sure, but based on Bob's description .....
K&B made the so-called "Greenhead" up until about 1961.
In 1961, the introduced the new design, the "Series 61" engine that has the bolt-on front end with ball bearings that is still they standard design. The Series 61 35 was a steel piston/liner (whatever the material) aka known as a "slug" p/l. I believe the Series 61 was only available in 29 and 35 sizes.
In 1964, K&B introduced the "Series 64" which was the first of the Dykes-ring engines, but only as a 40. I don't think the 29 or 35 was made any longer.
K&B in the early 70's brought out the Dykes-ring 35 as a plain-bearing engine. Still a good motor but not the equal of the slug engine.
And so forth.
The early engines, the "slug" 35's, were very good running motors if properly broken in, easily equaling or bettering any of the competition. But they had a propensity to break crankshafts and HAD to be properly broken in. The old saw then was "Three K&Bs: One to fly, one in the mail back to K&B for repair, one in the mail back from them.". I ran them a lot in the early days after college and personally never broke one, but my friends had other experiences.
From Bob's description, I suspect he was using a slug 35.
Regards,
Bill