It could be a .45 or .50. I'm pretty sure all the .61's were ringed, as were the .50's, possibly Dykes rings at the top edge of the piston. If it's ringed, there will be some "windows" in the exhaust and bypass port. The .45's were lapped, iron piston. Of course, they started out as Veco, became K&B & then became RJL/K&B.
Early Veco's were made by K&B under contract and were basically early Greenies. Clarence Lee was the guy that designed the later Veco engines, after Veco took over production from K&B. I don't know if he designed the "Series 200" Veco engines, but did a prototype speed .29bb I recall seeing pictures of, plus the .45 and .61. Maybe the .19bb, too.
Mr. Lee still advertises occasionally in that AMA magazine's classifieds.

Steve