Marty -
Never personally dealt with Dallee - but they've been around for years; I am sure that if you call them and describe your GG1 with it's shell removed they will tell you what you need and offer some advice.
All Williams GG1's came/come with DC can motors (they look like little cans, usually aluminum in color) - as does almost anything Williams has ever offered, BUT:
Back in the old days (1970's) when Williams was getting started, they offered
kits and such (not real familiar with them) that were designed to use old Lionel
AC motors, I believe. Not sure about the GG1.
Anyway, take the shell off (4 or so screws, I would think), take a look, call Dallee
and discuss it. I guarantee that instructions are included with the kits.