Try the EBC Y503G,it's probably the best option for the TW and they are grooved too.
Also make sure to check your brake pedal free play before replacing.
Rear disk conversions have been made, but they are one-offs.
You will need to fabricate a custom hub,which will probably cost a few hundred bucks.
There is this kit also,but I couldn't find any info about it or a review,even in japanese.