The following image shows the plastic chassis frame from the Donor Bachmann deltic following an attack with razor saw, large file and 120 grit wet or dry

I started by razor sawing off a section from the ends of each tank end to reduce the overall length of the tanks so that they fit within the "lip" on the inside of the Dapol sides. The tank side faces were then sawn off as close to flush with the frame sides as I dared. These sides were then filed flush and the bottom edges of the tanks were filed down so that the raised detail was removed. Again this is so that the Dapol sides fit over and around the remaining original assembly. Hopefully you can see the areas that have been sawn/filed against the untouched standard finish.

The weight will be trimmed accordingly once body and chassis have been re-united and fit confirmed.

EDIT:

here's a picture with the frame assembled to the chassis, you can see how much of the weight needs trimming at each end. I will paint the ends of the weight the same colour as the frame to disguise it once it all fits together