While restoring my 69Z I noticed the subframe rocked when laying on the garage floor. Closer inspection found it bent up an inch. I found a
70 Nova power disk brake subframe a mile from my house. How lucky is that? Quesiton is are they exact duplicates or will I need to do siome modifications???

They are virtually identical.

Buy it, if it's straight.
If it's bent also, you can have the original straightened.

Here's a picture of the subframe dimensions from David Pozzi's web site. They're the same as a Camaro even though it says Firebird.
Subframe Dimensions (http://ourworld.compuserve.com/homepages/David_Pozzi/F_gen_Firebird_sub.jpg)