I modify DDR3-BL, SS-3.0 and SS-2.0 kits from Knifekits. I re-shape the frames and blades, do extensive filework, and other embellishments. Often I make new damascus blades, and bolsters in damascus or mokume. I change a lot of the assembly screws to gold plated or black oxide types, and file work the pivot screws and the buttons, often adding a matching faux left side button. As said, the tolerances are tight, so having the liners and parts all together in one batch is simpler than me making them from scratch. Then I finish them up with mammoth scales or high grade burl wood and they are really nice custom automatic knives. Others I fit with Micarta or G-10 scales for LEOs, military, and paramedics.
I haven't done it, but I think you could convert one to a leftie button with little more than a counter-top mini mill or a good drill press. The frames provided are easily reversed. The bolsters would be the only parts to modify.
I would suggest you get a kit or two from knifekits to see how they are make and work. They have three sizes and a couple different blade options. They sell all sorts of BL and auto parts and springs, as well as the matching drills/cutters for making the spring pocket.
