For those who have long tubes and scrape everywhere.... why did you buy long tubes ? Mid length headers are the best of both worlds. Long tubes are a giant pain in the butt and don't net you any better performance on most engines then a mid length or even some shorties.
So I investigated with real people who did the Hipo/351 swap. All of them reported better low end torque, better apeal on "stock" looks, and none said they could feel any difference in top end. This was backed up by a dyno run at Dallas Mustang. The car actually made more torque up to about 3000 RPM with cast iron maniafolds over long tubes. It did lose a few HP on the top end, where most of us wont use anyway.
Because the dyno tests done at Modified Mustangs & Fords show the opposite. The HIPOs did not make a difference on the performance, compared to logs. Headers gave some 10 HP increase. That test was done with a stock 302 with 2" exhaust pipes and generic passenger-car mufflers.
I was going to wash them with Dawn wipe them with prep solvent after that and then use UHT paint.