M_Boats: Mainsheet System

I am having trouble (215 lbs & 81 yrs) getting entangled with the present setup of the M15 yoke Mainsheet when trying to lower my motor (3hp Yamaha):-( Giving thought to converting to a 4 part Mainsheet System attached at the same points presently used at mid boom and just in front of the hatch. Has any one tried this and how has it worked out? I am slightly concerned that the present Stern Yoke System may be giving the mast some support that it would normally receive from a backstay. Jerry M. any thoughts on that? George Merry Helen II M15 #602 'We Can Not Control the Wind But We Can Adjust our Sails'