Having not flown a glass panel, Im not sure if my opinion will be of much help, and I cant comment on the transition, but I thought I might as well throw it out there.
As a current CFII at a very large flight school, and have trained students who take long breaks in their instrument training, I can say it does really depend on the student. I have had students who are able to pick it right up after one review in the sim, others are having to start right back at square one. My suggestion is to do as much home study as you can, jump in the back seat of another training flight as much as possible, and do enough sim flights to get your scan and procedures back before spending time and money in the airplane.
Good luck