brushed/brushless question

[the mad1]

i have only just come back into rc cars so i am trying to figure out brushless but i have a load of brushed motors from when i used to race years bk that have only done 3 meetings but i have now bought a speed passion feigaio brushless system with a 13.5t and i was wondering if i can use my brushed motors on the speed passion if so what is the limit for brushed motors on it.
also is there anything i have to do to run the brushed on them or have i just got to bite the bullet and go buy me a 7.5t for my xxx

also i was wondering what is the brushed equivalent to a 7.5t ?