I believe it involves deleting the bellhousing adapter plate and changing out the mounting bracket if you go with the Mendeola. Relatively minor differences that can always be done "down the road".When you order the GTM kit, they will ask whether you plan to go with a Porsche G50 or the Mendeola SDR transaxle. I believe the chassis set up is slightly different.
When I went through the configuration for my kit in April, Jason asked me about this. I said I was going with Mendeola, but if that went south then I'd go with Porsche. He indicated that wasn't a big deal, they would just have swap out some parts if I went that way.