IM wheelsets will definitely not work in Lionel roller bearing trucks. IM makes only one style of wheelset that I know of. It is 33 inch wheels and needle point axles. I don't know the length without measuring, but they are an identical length to Athearn, Weaver, and of course the IM wheelsets that come in the kits with plastic axles. They are very; nice and add a nice amount of weight. The roller bearing trucks need blunt end axles.
A word advice, get a wheel gauge. the most handy one is sold by the NMRA. It can be use to check wheel gauge and coupler height and a few other things, and the ones I have even have some gauges for 3 rail stuff.
Since 2 rail is a little more precise than 3 rail in the wheel/track structure, you need to make sure the wheels are in gauge and the track for that matter. Sometimes brand new wheelsets come out of the box out of gauge. About 10% seem to regardless of mfg. So you should check them before installation.
It is pretty; easy to adjust the gauge, especially if too wide. the insulated wheel usually slides on the axle fairly easily. I put some protecton on the axle ends, and then put the set in my vise, and slowly tighten while holding the NMRA gauge on the wheels.
