You need 2 TZ85A as they only drive a single motor each

The alternative to the GR02's is some cheap and cheerful drill motors from Argos or B&Q
http://www.argos.co.uk/static/Produc...er/7112946.htm
http://www.diy.com/nav/fix/power-too...skuId=11448297

There are a number of posts on the site relating to different mounting methods for drill motors