Honestly I dont see why not. I could buy the exact same kart off of him with the same engine. If I’m not mistaken, my X30 was from J3 (Compkart) via Supernats. Jerry buys a bunch of their stuff for his clients at the end of the race.
Maybe I am naive but I think you could, with enough $ spent, have the same equipment and engine parity.
Edit for clarity: My engine was cheaper to buy used from supernats than new from builder. This was not out of the box. I paid less than a new x30 on Comets site. If a built engine is same/cheaper lightly used than an unbuilt new, that makes the value proposition weird. I would always go with the built engine bought from a team, for me it seems a better deal.