I know that the 727 big block tranny cases from the early 70's and the A518 tranny cases from the mid 1990's are both cast aluminum, but does anyone know what type of cast aluminum alloy each of these are? I've got to do some serious welding on each and was wondering what TIG filler rod to use on each for the best results?

Otherwise I'll just start experimenting with 4043 and go from there.

Thanks!!!

Mark