I have a series 3 2.25 swb I thought they were capable of towing 3.5 tons yet the plate on bulkhead says only 2 tons is this correct?

I think the 3.5 is the gross train weight. If you search on this forum you'll find lots of info and I'm sure someone will be along soon who knows all about it.

Welcome to the funny farm and be prepared to laugh at yourself 'cos they all take the p--s on here.