Cycling and large leg muscles are opposite no chance. In other words get down to the gym but you will be doing opposites. IE cycling equals stamina muscles, think Paula Radcliffe and weight training equals arnold schwarzenegger you will never be able to be both. So based on what you wrote you could not be an arnold schwarzenegger if you tried.
One option is to pick a hill, pick a gear hit the hill in a gear that wrecks you quickly. ie you are totally exhausted as you would be If doing weight training. You should not be trying to get up the hill. 50 yards up the hill maximum. Mark the spot turn around roll down the hill this is your break as in weight training. Do it again and again each time you will manage a smaller distance. You probably won't manage 10 unless you change the gears (or in weight training reduce the weights)
Over time you will start to pass the mark regularly (50 yards might be to far. So note the time it took, in weight training 2 minutes). So now it is time to use a harder gear. Always do it standing up to work Quads and hamstring equally.
This is what I had to do but on an exercise bike to rebuild the muscles in one leg. An injury resulted in septic arthritis in one knee. I have to do none impact and non weight bearing exercises ie cycling sat down. As I am dependent on a bicycle not that big a problem. Initially, I needed help to get to the toilet so an exercise bike was a necessity. You can obviously use an ordinary bike.
I wander though if you have the genetic makeup to achieve a significant and therefore noticeable increase in your muscle mass.....only one weigh to find out!