Bill,
If you're not into soldering or tinkering there are other choices, although they're not necessarily prototypically correct.
Lionel has made in the past:
1.) For Steam -- Tenders fitted with RailSounds to replace the one that came with your locomotive. Two examples are Prod. No. 6-18333 (like the postwar 2426W) and Prod. No. 6-16655 (like the postwar 2046W or 2671WX). Both of these are older (c.1990's) and have original RailSounds. There are newer ones that have what is called TrainSounds instead as well. The sounds are reasonably good but if you're a stickler for accuracy the chuff doesn't synchronize perfectly with the position of the running gear on the locomotive.
2,) For Diesel -- Boxcars fitted with RailSounds to pull immediately behind your engine. Like above but with Diesel sounds. An example would be Prod. No. 6-17214. This specific one is not traditional-sized though, it's scale-sized, so it would look big when placed next to your postwar diesels. There are others that have traditional sizing, and also TrainSounds versions like the steam TrainSounds version mentioned above, that are newer.
I have one of each, tender and boxcar, they were the first RailSounds equipped products I ever had, and I'm still greatly impressed with them even though RailSounds has evolved significantly since they were introduced.
These tenders and cars are much less trouble than modifying your hardware, but you may prefer to go the modification route with ERR as @modeltrainsparts has suggested, for better realism.
Mike
