Luluscotty

So, I have found a used but decent 90 200TDI chassis, hoping I can fit this as a replacement chassis for my rusting and MOT failed 300TDI. What would I have to do to ensure the 300 engine and gearbox will fit back into a 200 chassis ? I'm hearing that the only differences are the engine and gearbox mountings, so could I cut out the old mounts and either bolt or weld these on as part of the new chassis prep ? Any thoughts or suggestions gratefully received !