SANDERSON HEADERS

Question guys...I'm in the process of rebuilding my 65 Barracuda 273 LA V8, A833 4 speed, with power steering and considering installing the Accurate brand, original style Hi-Po exhaust system. If i wanted to add headers are the Sanderson short headers same length as stock manifolds in order to match up to the "original" style exhaust header pipes? Also should I do this with the engine out or installed? I'm new to this so I'm learning as I go.
Thanks