It's been a long time but I think most of them were just 2x6s a couple feet long or approximately the same size strips of plywood with just thin furring strips screwed or glued to them- probably just construction scraps. I want to say they had some strips on both sides to help prevent slippage but again, that was a quite a few years (and brain cells) ago and I doubt I ever took any pictures with them; I'm not even sure where most of my pictures from that era are anymore. I remember everyone around always jumping in to help each other though- get the snow away from the wheels and from in front of any undercarriage parts so you're not trying to push snow out of the way, get some bystanders to push and I don't recall us ever having to call a tow truck or snowcat. You could always add some sanded paint* to them to make them extra grippy and more weather resistant but I'm sure they're not as effective as some modern Maxtrax. There's a reason why skiers and climbers used to be called bums and dirtbags back then, most of us didn't have dad's credit card, had older vehicles and we made do with what we had.
*Add play sand to whatever can of paint you happen to have left over, shake well and paint with that.
ETA- I googled "wooden traction boards" to see if I could find any examples but most show through-bolts. That seems like it'd trash your tires first time they spun, no bueno (maybe I'm wrong?). I found this video and it's a good idea of what not to do: The diagonal grooves aren't going to do squat, no idea what the idea was behind that. If I were going to try that, I'd diamond checker them like a pair of handgun grips maybe but even that seems like more work. The other design has the spacing too close together, you want the tires to just drop in between the horizontal pieces so that it's pulling the board under the tire while riding up onto them. His were effectively no better than just a plain board, which obviously wasn't going to work in that slop.