Well, I guess you could wire them in parallel to get a 160 watt transformer. However, you'd have to tie the speed dials together somehow. How old are they? I've heard that the old school lionel transformers were rheostat-controlled, whereas newer controllers are probably pulse-width-modulated (transistors). Honestly I'm not sure I'd trust either type hooked up as two units back to back.
But, if you can get them open, you may be able to make them work. If you take the actual transformers out, merge their inputs (from the wall plug) and their outputs (to the rheostat or PWM), you would have double the wattage. But I'd be surprised if the control circuitry (either kind) could take double the wattage it was designed for. In a PWM system you may be able to piggyback the transistors (desolder the transistor from your donor unit, solder it on top of the transistor in the other unit, I've seen in done in R/C cars). In a rheostat system you could probably source a higher-rated rheostat and swap that in. But I still wouldn't trust it. Besides, the finished product would push way more than the locos need. I don't know if the current would be dangerous to you, but a short circuit would put a huge strain on your wiring, your hacked transformer, and whatever caused the short. This in turn could cause fires, melt plastic, fry electronics, the works. I guess you could put a fuse in it, but I suspect you'd be replacing that fuse pretty often.
I'm all for hacking stuff to make it work. But in this case, I'd say just get the right part. (You could probably sell the 80-watt unit to contribute to the new unit.)
