My factory seat cracked so installed a $40 Ebay Kirkey circle track seat and $20 3" 5 point Simpson harness. I didn't like the way it woulds have set in there(kinda tall) so I made a lowered seat mounting bracket from more angle iron. It lowered the seat about 2.5"- 3". I now set back a couple of inches further too allowing a little more head and leg room. I also installed heavy duty hinges to allow the seat to hinge forward over the steering wheel for easy access to the engine exhaust area. Again, this is my version and works well, but there are probably better ways to do it.
I had this installed when I did the double end over end(ass over tea-kettle) manouver. It kept me very secure and safe(other than sand up my nose, LOL).
Key words for searches --- Honda 350 FL350 FL350R FL R Odyssey racing seat install installation mod modification seat belt simpson replacment