You can do a rear disc conversion, but nearly everyone has stayed with the drums, brake bias is more towards the front anyway, so save the money and invest in some decent front brakes.
The only problem you will encounter is that there is not enough room to run a exhaust system down by the gearbox as far as i'm aware, nearly everyone has a side exit. To upgrade the power it will be same as any other 4efte engine
I have a done a rear disk conversion on mine !! pain in the *Ss