Matt, in getting back to your original question, Chevelle mounts on the frame and on the engine and the SBC will bolt right up.
I myself am also new to this forum, and also have a 70 model LeMans that I am putting my built 400 SBC in. My car came without any motor or transmission, so I do not feel prone to keeping the car Pontiac powered.
Sometimes we have to play with the hand we are dealt, and since its Your Car, You can do what ever you want with it.
I have ran SBC 400 engines in several cars, and they are in my own opinion, the best of the small block engines for low end Torque and cubic inches.
For those of us living on a hobby budget, then we can use whatever we have available.
My car is still a Pontiac, and it will still be powered by a GM engine, so I have no regrets in using my SBC.
To each his own.........
Jim C.