Boston Qualification

I have run over 30 marathons over the last few decades. I gave up my attempts to qualify for Boston until I watched my wife take up running in her 40's, run a marathon and then run a marathon fast enough to qualify for Boston. She ran Boston last year so we experienced the bombing first hand. Now, at age 50, I need to run a sub 3:30 to qualify. I didn't realize what chasing the unicorn meant. myfitnesspal has helped me lose weight. My weight has contributed to keeping a BQ out of reach. When I was younger, running a sub 3:30 was not hard. Now that I am 50 I am trying to picture running 8 minute miles again. I am officially chasing the unicorn now. I am 6' tall and weigh 195 with the goal to get to 185 before I start training for the Twin Cities Marathon this fall. Any suggestions for this older runner? Should I try to get down to 170? Do I risk injury doing too many miles or too much speed work? Running Boston has been an unreachable dream for so many years. I want to go back to Boston as a RUNNER and not a spectator.