Questions re: scale to 3-rail conversion on K-line freight cars??

You can just remove the 2-rail couplers and swap out the trucks for K-Line 3-rail truck/coupler assemblies. The existing mounting holes and screws are fine. As I recall you have to take the car apart because the trucks mount from the inside. The late production, highly detailed woodside reefers have lift-off roofs so that makes it a little easier. I think the top of the truck screw is sort of hidden under the ice bunker (It's been a couple of years since I replaced a truck on one of those cars, so my memory may be a little off). There may also be a little plastic filler plug in there to hide the screw head when you're looking at the interior. The newer style K-Line trucks without the thumbtack can be a bit hard to find and pricey, but I'm pretty sure the old ones will fit. You can probably use other brands of trucks, but I've never done it so I won't swear what does or doesn't fit without modification. 

When K-Line went out of business, Justrains bought up a bunch of the leftover 2-rail reefers and converted them to 3-rail because they had too many to sell in 2-rail. You still see them occasionally on eBay or at a train show, 3-rail cars in a 2-rail box. 

Joe,

I purchased some of the Justrains 2-rail to 3-rail reefer conversions, and the converted reefers sit a little higher than the 3-rail reefers.  This is noticeable when you run 3-rail and converted reefers together, but it is acceptable.  K-Line made very nice reefers.

Ron

Ron makes a good point. I had heard that about the conversions, but I neglected to mention it in my previous post. It wouldn't be terribly difficult to correct the ride height with a file or a Dremel tool if you want to. 

Here's another thought: If you have Gargraves or other square-profile track on your layout, you can run the scale wheels. If you plan to run the reefers in a block, you could put a Lionel-type coupler on one end of the car at each end of the block and leave the original couplers on all the rest. I am fairly sure that you could just add the 3-rail couplers to the 2-rail trucks; I think the K-Line 2-rail trucks have the coupler mounting block.

Also, most of the Kadee-style 2-rail couplers will actually couple to most Lionel-type couplers. I haven't done it enough to say how stable the connection is; I've been told that if the trackwork is decent they will stay coupled. Might be worth a try before you go to all the trouble and expense of converting. Of course, that's only if you have square-profile track; scale wheels will actually run on tubular track but will not navigate switches.

Another tip - if you have any 2-railer friends, or if there's a 2-rail club around where you live, you might just find a 2-railer who wants to swap trucks. There are always 2-railers who bought 3-rail equipment they couldn't find in 2-rail and are eager to trade. I've gotten quite a few 3-rail Atlas trucks that way. You might also check if Atlas trucks will work; if they will, that opens up the possibilities considerably, either to buy or trade trucks.