I also dropped 500 on and lightened flex plate and a G on a Yank preformance converter, they adjusted the price because I didn't use the converter that they use for the tranny build. Yank converters and Gearstar work hand in hand. They both built my order.
Once the converter was built, they drop shipped it to Gearstar where they installed it on my freshly built trans and they tested the 2 components together to ensure proper function. After that they shipped the trans with converter installed and filled with fluid ready to install.