That Diamondback already has a mix of linear pull and cantilever brakes. There's no way to know from the picture provided if the brake levers themselves are long- or short-pull levers, but the braking system may already be mis-matched to some degree. You can get Tektro "Mini-V" brakes which are more compatible with traditional short-pull levers than normal linear pull brakes. The Apex's frame already has a rear cable stop along the top tube, so you could easily put a linear pull brake on the back to the match the one on the front. Or...move it back to cantilevers front and rear.