I had a crappy fitting set of early-design hooker comp+, and the right side was a miserable install. I put my engine in with the right header installed without an issue, and I could have done it with both headers on it.

Based on what I have seen in the last decade of interacting with hobby car guys, I would strongly recomend installing the engine without the headers attached. But if you think you're a badass, go for it. Keep in mind there is a big difference between thinking and knowing.