I did the same swap to make a better representation of a Southern 4-6-0. The smaller tender does a great job of changing the looks entirely on this engine. See this OGR forum link Correcting Lionel Southern Railway Colors (plus) | O Gauge Railroading On Line Forum (ogaugerr.com)
The new legacy electronics are much smaller and were no problem to transplant.
Does the new electronics have a grounding issues as well.