F-body trans and header install wich 1st?

I have the trans out for fresh non lockup 904 to put in my 78 Aspen with 340, also all the exhaust is out for new Hooker competition headers. Debating if it would be easier to put headers on now with trans out or trans in then headers? or maybe it doesnt matter?

I would put the headers on now BUT leave them loose
in case you have to spread them for the trans install

With my Aspen it has been a lot easier installing the headers 1st then sliding the trans. And as Mr P body stated leaving them loose. What size headers are you going to use? 1 5/8 or step up? When I installed a low profile Milodon pan on my 408 I have to istall the engine 1st because of clearance problems with the pan.Incase you go that route in the future

They are the 1 5/8, getting headers in loose is a good idea. Sure was nice pulling trans with nothing in the way. Thanks