Sorry for the delayed response to your question. I was out working on my ranch and my reference material was back home. According to the work done by Ned Schwing all prewar Model 61’s that were either Routledge or Winchester Counter bore barreled had matted to receivers. Post war rifles, after SN 120,000 will have a either a smooth top receiver or after approximately SN 214,000 will have a grooved top receiver.
I hope this helps.
Model 1892 / Model 61 Collector, Research, Valuation