No, you can't magnaflux aluminum heads. Here is a link that describes how to check aluminum heads for cracks:
http://classic.artsautomotive.com/crackcheck.htm
You should also use a straight edge across the head to check for warpage. I don't know what the tolerance is for subie heads though.
Type: professional, shadetree, maintenance
On what: lawnmower engine to caterpillar. prefer chevy, subaru, rotary engines, honda (yeah i know)
How Long: 13 years
Other Skills: too many to list.
I'm not new to subarus but I am new to this site. I'm from Tacoma and it seems like there are a lot of people on here from western washington. I just took ownership of a sweet 85 gl10 turbo. I actually like it more than my last subaru (03 wrx). I'm looking forward to learning more about and contributing to the awesome that is subaru. So..hi.