I pretty much agree with everything stated above. All good advice. I would suggest you join 'bigblockdart.com' LOTS of good info on their site.
As others have said, they are a pain to work on. I did a RB in a '68 Valiant a few years ago. All stock inner fenders, suspension/steering/etc. The TTI headers were used and fit well but a real &##$%@ to change starter. I would go with the ARE motor plate at the front. Gives more room in the header area.