So, I've seen a couple V-twin diesels installed, (kinda loud), and one 4 cylinder Kubota, (kinda big), but all with the T-20.
I just started my project. 3 cylinder Kubota D-722 20 HP diesel. No clutches or T-20 will be used. It'll be hydrostatic drive. If that's not enough, I'll be adding a turbo to the Kubota and turning up the fuel. It'll sit below the body and keep the rear seat.
Should be fun. I'll get some pics this weekend.