Hi!
Sorry! Of course the old .19 Veco is a lapped engine ...I'm getting old...!
The newer .21 Veco version had a ring and Mc coy made some trim piston/liners for this engine I recall...

All engines should be run-in with their carbs drums wide open just because then you know that the engine will get enough fuel (which means cooling).
When you run an engine on low rpm using the throttle drum to adjust rpm...you just dont know if the engine gets enough fuel....at least it is harder to detect.

Regards!
Jan K
Sweden