Nowhere did I read what the mfg. date for the gun to be converted was. I would be real careful here. Just because today's 336s might handle it, doesn't mean a 50's mdl. would. I have a early "origional" ballard cut rifled one and wouldn't dream of trying this to it ('52 I believe) anyway, my point is just because a 2004 list says the guns are the same, it probably means 2004 guns, not earlier ones. I'm sure Marlin had no intention of using ctgs. with 50K pressures when they first made the 336s. Better safe than sorry. How about a 35 Krag (short?)? I remember a Guns article about a guy using the Krag case in 30 cal Lefty someone if I remember right. Check the deminsions, might be possible