I agree.....
Propane has the potential to kill you and your family....... Take it seriously....
Use only materials approved for propane. Learn proper installation practices or hire a professional.
Get as wild and crazy as you want with plumbing, paint, layout whatever...... Electrical and propane are a different story. Do it by the book or find a pro to help.
As to regulator choice, I would check with your generator vendor and get specific requirements from them. I did a little Google-Fu and did not find any clear answers.
Regarding your engine? Is it a Cummings four stroke or a Detroit two stroke? Both were available in the Gillig.