early A slant header

Make a copy of the Hyperpaks out of Header tubes. Even a muffler shop could make them for you for less than a set of Cliffords. Just give them the Ebay flanges.....Doug said the capped riser side flowed as well as the fronts, although it looks like it wouldnt.

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The advantage of the cut-and-capped manifold is that you retain a hot-box which will mate to the Offenhauser intake, giving preheat for cold climates.
You're right, they don't look like they would flow, almost to the point in my case that I was just going to leave the standard exhausts and be done with it, nobody in Australia can guarantee their headers will fit or work with early A-body car, or with left hand drive.
How good do those Hyperpack Headers look! I saw that pic elsewhere on the 'net, they were my screen-saver for a couple of days.
I can see they've had a bit of a welding repair done but who cares, the owner is a lucky man! I don't know why someone doesn't do a run of these and we can chuck all this other stuff in the skip!
Or maybe someone (Hint, Doug Dutra!) can do a run on rear pipes that will fit properly and eliminate the modified standard pipe?
I like your idea of getting a muffler shop to do a tubular equivalent, that's got me thinking.
Regarding the Cliffords, they look like they will fit well, they really look the part, but trawling through FABO posts (some very old ones, c.2006) there was a few really negative comments about them: poor fitment, lack of willingness of the manufacturer to assist, took forever to supply them. Maybe that has improved?
Are Dutra Headers something which can be bought new or are they a period speed equipment item and I need to search for it on eBay? Do they supply a 'Dutra-Prepared' rear pipe, or do you do this yourself?