I don't think plans exist ,could be wrong. Ever since I'v seen the HR1 I wanted one. I emailed John Harmon about plans and His reply was something like "no". So I have read everything i could find, Fastback, modified firewall(sorta like HR2) IO360 angle valve. One thing was apparently the visability isnt very good.So my decision is to either build a very light -3 w/IO340 or a very light -4 single seat clipped wings (HR3), Fastback, IO360 parallel valve 2900rpm max, wood prop.