Does not matter the position of the engine,if you want to fit a small v6 and you put your mind to it,it's possible!
From what i've measured any flat four below 2litres,with 8 valves(so only 1 camshafts on every side) could fit nicely,but you have to make new engine mounts,and an adapter plate between the gearbox and the engine,or fit a longitudinal gearbox with new driveshafts,or change the rear axle and make it RWD