If you have trouble finding them thru sponsers on here Alternative fuel trucks use them for vegistrokes
Not sure if they are smooth enough for your high h.p. applications
Try:
Dino fuel Alternative .com
Veggie garage .com
RDS in Fl. makes tanks for vegistrokes (now biofuel tech.) I have a 30 gal tank in my 03. Excellent fit and the fill spout is cool (fits in passenger door).
Also make a 40 gal. Dont know if you can buy direct from RDS.