TCI and other companies have been selling complete frames with suspension and 37 degree brake lines for decades. It seems to be the hot rod standard. The 37 degree fittings will not be a problem and neither will the aluminum fittings. The residual valves are always aluminum and usually from Wilwood. I chose to use 45 degree double flares with stainless lines and stainless tube nuts on my car, but other fittings are aluminum and brass. I have all Wilwood products and the fittings they offer for various uses may be brass or aluminum. Stainless steel is NOT an option. For example a 1/8" NPT to 45 degree flare fitting will be brass, while the adaptors from the MC to the 45 degree flares will be aluminum. One problem with threading together two parts made from SS is galling. If you don't use anti-seize on the male threads, they can gall and you'll never get them apart.

SS tubing is the best product out there, with regard to looks and longevity, but it is hard to bend and hard to double flare. I bought some Nicopp tubing recently and agree that it's easy to work with.