You can go bigger, I ran an F-cam in the cougar (it has one in it now)I also had an E-cam in the car, it picked up 20rwhp with the F-cam, however it moved the torque peak up 1,000rpm, hell the mustang has a .577 lift cam, 1.97" intake valves and a stock shortblock and it clears.
Is it a HO motor? if not, none of the cams will work. Is it speed density? If so none of the cams will work.
If it uses a MAF then I would go with an E-cam, but you will need a converter or some steep gears, with any of the cams you are going to lose bottom end over the stock cam.
Rob