The 36 engine makes a big improvement over a 320 engine. It's around a 3-4 sec improvement in the 40-80 increment and the torque feels stronger everywhere in the rev range. Admitted its a bit clattery at idle but boy does it sing when you wring its neck. It has a much harder edged snarl to it , even with the same exhaust system.
These engines were hand built with forged internals and short skirted Mahle Pistons with very thin rings, real race engineering but consequently can vary in the power stakes between 260ish to 285ish BHP if the cam timing has ever been messed with!
I will give one thing to the 320, it's so smooth refined and quiet that if that's your thing keep it stock!