Have a sentria that has been sitting in my garage. Had the intention of turning it into a Hentria (Heritage bag w/ a metal fan) but was busy & preoccupied with other things. I know something has to be done with the front bearing plate to get a 500/Classic-series fan to work in a G-Series, but can't remember what procedure needs to be done. Who can give me a breakdown on what the procedure is to retrofit a metal fan in my Sentria?