Steel or aluminum motor plate!

I have a aluminum motor plate and mid plate. My 67 cougar is close to the but not same as mustang. I have a mustange II front suspension I install and remove the sock towers to give me more clearest for my 460. But the motor plate is not tall enough or made low enough to mount to my frame brackets. I have some 1/4" aluminum and some 1/4" steel plate. My concerns is I can fabricate in either, but would perfer the aluminum. Not sure if adding about 4 more inches to it would weaken it, any advice welcome.:rolleyes: :HMMM: :HMMM:
And whats the best what to cut aluminum, It just eats up my saw blades?