front and mid motor mount plates

[57sailplane]

hey guys,

i was looking at summits site for front and mid motor mount plates for my sbc. i see they come in steel and aluminum. i would think the steel would be best for the mid plate cause of fitment issues with the tranny but not sure what will work the best. what do you guys use. both aluminum or both steel or do you mix and match. also do you bolt them directly to the frame.
again your help is definatly appreciated.