You can certainly MIG aluminum, but I don't think it would be the best choice for a manifold. Mainly because you need a fairly industrial machine to get the job done right. Yes you can do it with a Lincoln setup from Home Depot or something, but you aren't gonna be able to get the heat you need. Also, it doesn't work very well unless you have a spool gun, which cost $$.
TIG is just a lot easier setup, the welds look better and you can control your heat a lot better.
TIG is just a lot easier setup, the welds look better and you can control your heat a lot better.