Heres my old one, just to echo what the lads have already said buy a secondhand bachmann cl 20, sell the body on ebay or another site (you'd be surprised how much they tend to go for ).
To get the body to fit the chassis a few mm at each end needs to be paired off. Theres loads of decent pics in the net and if your stuck i ll send you on a few close up piccys. The class 20 chassis will easily pull a full realistic rake of coaches around any layout.