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A few years ago I hand fabed a tuned length V8 manifold for my 30 year old girl, to suit propane
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ARGH
Don't you know better???, Women are complex enough to deal with, without bolting new headers on them and adding propane!!.
Alodine is a good idea, one common ion laser I worked on for 20 years is Alodined, and it makes a very tough, hard to scratch finish, much nicer then blank anodize. In other words done right, it holds up.
Watch out for the hexavalent waste, don't get it on you. Not exactly some thing I'd dump in my drive way to evaporate.
Steve