I have had no problems with my Hooker 2457's other than the ARP bolt issue you mentioned. Original BB car. Is that a stock motor mount on the pass side?
That is great that your Hooker 2457 Competition Headers Fit, the ones I got from Summit did not, I tried to be very accurate with what I wrote.
My Car was a 350 cu in and TH350, trans was gone when I got it, I got the Correct Frame Mounts from Ricks, and the Motor Mounts are Energy Suspension, measure out to what info I have seen.
Do you have Power Steering ? and your 2457's are Competition Headers with 2" Primaries ?
Also, I have looked at many Pictures of the 2457's, the Profile/ inset of # 5 on my set was even with # 3.
If you go to Matt's posting for "Evening with the hookers" in the Bench Racing group, Posting # 44 shows a set of Hooker 2457's Competition Headers where # 5 Drops straight down Behind the Steering Box which is Manual
, Mine has Power Steering
Last Picture is from DavePL on "Camaro Tech", He wrote SuperComps do not fit, The were 2457's - Competition and that is what My Install looked like, # 5 hit Right on the Power Steering Box and my Bolt Hole for the Motor Mount to the Frame Bracket was about 7/8" off.
And all I'm trying to show is how the Doug's D320's fit for my Install, I'm glad I borrowed a Dummy 396 Block and heads for my Mock up, and that your 2457's did fit.
I'm sure there might be a Doug's D320 set that does not fit, I feel I have all the Correct Parts for the Power Steering Install.