There are numerous "recommendations" on torque into aluminum. For example torqueing down aluminum heads in high performance applications. From the recommendations out there take your M8 torque down about 3 pounds from the cast rating. All of that depends on what grade of M8 you are using. The specs are for the bolt shaft size- not the hole.
Since you are installing a non-critical part, get it nice and tight using anti-seize compound on the threads. That is the biggest issue with steel into aluminum. It's called galling. It will feel like you are applying a lot of torque as you tighten, because of the heat expansion against the aluminum, when in effect, you're just messing up the threads. On your TAV plate, you could get by with plain old grease and German torque. (Good-N-Tight)