take overall width measurements of each seat and locate race seats that are similar or maybe a little wider since we have a little room. have someone fabricate some brackets for them. on instagram a user "thesmartcar" had it done so you can check them out. The seats nearly touch in the middle if I'm not mistaken. Lastly i believe removing stock seats throws a code so be aware of that. Other than that not a hard task
I have these seats in my Locost(home built lotus 7 replica). They measure 19" wide which is the same as the Smart seat. I'm happy with the quality. You definitely have to be on the thinner side. I'm 32 waist and it's a tight fit. Getting in and out of them would be a little difficult in the smart. Not sure how race you want.