Thank you for that info. While I am sure I "can" do it, it is great to hear from those who "have" done it! The car is a console shift. But the need to firewall modification is new info for me.
From what I read people didnt need to modify the firewall. it is just in my case the drivers side manifold did hit the fire wall. Now, that could be because I was using a 67 big block K member which could be different than the 68-69 K members or normal factory tolerances or the casting number of the B body HP manifold I used is a little different from some other ones.
I always planned on running headers. I have the TTI long tube ones and I had to shim the engine up so it would "clear" the factory steering gear. I still dont think I have enough room there but getting the headers on is a PAIN with the engine in the car. If the header ever needs to come out I would probably use the Borgeson steering gear since it is smaller and would give more clearance. Regardless, it would save you a ton of head aches if you had the engine and exhaust manifolds/headers on the K frame and dropped the body on top of them.