well I am actually inquiring for another vehicle, I have a 64 C/10 with a 327 that is a little over 400 hp, I have some headman headers on it right now but they are only 1 1/2 primary tubes. The motor revs up a little higher than 8k, so similar to the 302. It would be nice to pick up a set of those headers for it. The price on the website is like $1200 though.....a bit much for me. the hedman were a little under $400.
I'm guess that 400hp is flywheel? A 1 5/8" primary tube header would work fine with your setup. 5-10 peak hp is not going to be noticed unless you have access to a chassis dyno, your car is consistent at the track or a very fine tuned buttometer.. As for the reverse lockout I do not know of any long tube header where it would be able to be used. Just my experience & couple pennies worth..