I basically got real lucky , did quit a bit of surfing and the folks at Tejas manufacturing where I ordered venturi unit (the brass pc where propane tank attaches to ) were very helpfull.
The venturi unit comes predrilled with a # 61 orifice which they state is for high pressure propane and comes in several diameters .
The size of the pipe is 3/4 black gas pipe , I measured inside of my vertical smokehouse and made sure burners stayed six inches from the sides for saftey , and just built it to those dimensions .
I was expecting to have to adjust pipe length , get differant regulators , mess with burner hole size ( which I still might have to do ) but pretty happy with results so far .
Need to get unit inside smoke house and see what kinda heat I get .
To answer your question Dave yes there are alot of formulas out there , but my wee brain had trouble with them ...