Unfortunately this is one of the hazards of tinplate. The 600/2600 series cars have couplers 1/4" lower than the normally larger 800/2800 series cars. Where 2800 series cars line up well with a 263e, the 600 series lines up better with a 261e which is just a smaller shorter engine. I can't remember where it's at but there is a really good chart/explanation post around somewhere that makes things a bit clearer, hopefully someone else can post a link to it.
What I have found is that if you have car with the older style latch couplers instead of the box couplers there is usually enough wiggle to make it work. There are several different sizes within tinplate trains and some play together better than others.
