Threading works well into 1.7mm ally so that will be the easiest way with some defcon. So will go that way if i head down this path..

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I'm a jockey kunts...

get it tigged, with a water cooled tig welder, LF have one go see them

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Jesus Built my car, Its a love affair, Mainly Jesus and my hotrod

Does it? How did you do that? So clever!

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Huge range of extinguisher brackets for cars!

http://kap.industries/

A water cooled tig welder cools the handpiece only. It allows you to weld longer and use a smaller torch head body for the same given amps compared with a gas cooled torch.

Bolt the manifold down onto some heavy plate section and tig away. Roger clark has welded injector bosses onto his manifold so it can be done.
For less heat input find someone with a pulse mig welder. You have a faster travel speed which equals less heat input and end up with a half decent looking weld.

You are going to have to devise away to hold the bosses so that they align with your fuel rail.