Oh I agree- it won’t be easy either way.
I just think his odds of successfully clearancing that header and oil pan with everything installed is about the same as winning the powerball. I know that with my luck, if I tried making space with a hammer, a clamp and a tire spoon I’d probably ruin the header AND the oil pan and have to pull all of it out anyway. So, better to just pull one or the other first. Or both. Pulling it all after you’ve totaled $1k+ worth of parts will be really disheartening.