Installing headers -- While engine pulled or after re-installed?

OK, not trying to start a pie fight here, but the TTI's I put in my 67 Barracuda are the best fitting headers I've ever installed.

My 65 was more difficult, but they still fit amazingly well, I thought, given the lack of room in the engine compartment (which was never designed to run a V8 - that was an afterthought, and is why the factory 273 manifolds look so strange) and really were easier to put in and cleared everything better than the hi-po 340 manifold I ran for years.

Not dissing Doug's, as I've never run them. Maybe they're better, I dunno.