the spring direction matters;
as does outboard mounting of the series 30..
both is not optional I'm afraid
(you could install a reverse wound spring from a series 20 rather easily (since it's essentially the same as a series 30 just symmetrical)
but you'd still ruin your belts if you mount it inboard

(not to mention you'd loose about about as much power as you would greasing your belt

)
Soo
if you serously need an inboard mounted "series 30"'esque TC..
then a series 20 will be your only option (well apart from the maxtorque TC which is roughly identical to the series 20)
'sid