IF you are cloning a 1970 Challenger, you should invest in a Shop Manual for that year. Year one and others sell them and it will answer all (or at least most of your questions). Try the following site for additional information on the orignial Challengers:
http://www.hamtramck-historical.com.
This site has Posted copies of:
Dealership Data Books
Eng. Drawings
Virtual Library of Tech Service Bulletins
Pictures
Old Ads
and much more......
Check it out......