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

I'm going to pull the 5.9L Magnum in my '67 Barracuda to replace a leaking freeze plug and some other work. I'd like to replace the stock manifolds with headers, probably TTI shorties unless someone tells me why I shouldn't. It is a 4-speed car, and at the moment it has slant-6 torsion bars, which I may or not replace at a later date. I've read the that 1.04 torsion bars often require a little bit of percussive reforming on the header.

Am I better off installing the headers before I drop the engine back in (assuming I can even do that), or do it afterwards? I'm not pulling the transmission for this, just the engine. If I need to, I can also replace the starter with a mini-starter. I can't read the model # of the starter, but it's one of the ones that can be re-clocked, and not a full-sized one like used on the 318 LA engines (I don't know what starter normally comes on a 5.9L Magnum, this one was already on there).

I'm doing this by my lonesome, so I'm looking for anything that makes it easier.

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