I've got a super astute that I will be rebuilding soon...it has a TTC gear system so could probably accept mild brushless without difficulty.
No so sure about the normal astute...but could try a mild brushless...say a 10.5T or 17.5T. Anything more may ruin your drivetrain.
The pink Tamiya dynatech motor was a hop-op option for both cars I believe...that was a quality option! It's a 14T, so plenty I'd say for a 2wd of that era.
Grab it while you can!
http://www.tamiyaclub.com/trades_model.asp?cid=113450
Procat...see kaszal's thread....I think he managed to get a 8.5T brushless with some modification....
I hope that provides some starting points for you...
Get some pics up.