Cruz, looks like you've got room to spare. Use the cell with a reducer in the union, 1.25" off the 90 comming out of the heater, cut a peice of 2" pipe 2.5" to connect the other union to hte flw switch tee, then reduce the other end of the tee to the 1.5" pipe (the cell can count as the 1' of straight run required before the flow switch. (on second thought, work it backwards from the valve, at least there's rigid pipe to connect to) What's up with the flex pipe in the filter system?? , ie, why isn't it rigid pipe?? Why is there a clamp on the return valve inlet?? If your pool is new, sue them!, if it's older, looks like you could use a replumb.