Assuming your plane is a relatively unmodified (cough) stock TB20, why don't you download the Excel sheet:
And choose the TB20 that most closely matches your plane, and use those values?
That's what any CAA would do if your plane was on their register and you wanted a noise certificate.
It looks like your plane should meet Chapter 6 or Chapter 10 limits fairly easily.
You won't ever get below the german "erhöhter Schallschutz" limit, because that's for all practical purposes impossible, so you won't get the lowest rate, but usually there's only a 2 EUR difference or so between "Schallschutz" (i.e. having a noise certificate) and "erhöhter Schallschutz".
You won't ever get below the german "erhöhter Schallschutz" limit, because that's for all practical purposes impossible
I do 
MTOW 1406kg Chapter 10.
German noise limit (Schallschutz): 68 db(A) * (M-500) * 0.017 db(A) = 83.40 db(A)
German enhanced noise limit (Erhöhter Schallschutz): noise limit - 7 db(A) = 76.40 db(A)
My airplane was measured to produce 74.3 db(A) according to Chapter 10.
But you are right, it's virtually impossible. I only make it because I have an exceptionally low takeoff RPM (2400 RPM) and a high climb rate (turbo charged). Most of the noise is from the prop and a high MP / low RPM combination is just about the only way to get there. The reason it is that way is because Cessna replaced the Conti O-470 with the much larger Lyco O-540 (because of the upper camshaft so they could fit the retractable nose gear) and derated it to have the same HP as before.
I am still baffled as to what might go into boxes 13,14,15,16,17 when only one noise figure is available.
It seems like going for the "pre 1980" option is the easiest way - for the time being anyway.
From a cursory scanning of Part 36, 36F looks like the Chapter 6 measurement, 36G looks like the Chapter 10 measurement. So any Chapter 6 value would go into box 16, any Chapter 10 value into box 17, box 13 to 15 N/A.
Looks like he's given up...;-)
His problem is he wanted to understand rather than just do. There is no real consistency. You just need a plausible certificate.
Looks like he's given up
Who has given up?
Mine is all done, using the pre-1981 method
Laminated and gold plated
Come to Augsburg EDMA and test it. If it works there, it'll work everywhere. Make sure that my friend the noise certificate fetishist is on duty that day.
I make you an offer. I pay the noise fee if he refuses to take it, if you pay my 5km/h German speed camera tickets.
Do you think I should use a special font for the title?
This would look more the part:
if you pay my 5km/h German speed camera tickets.
Since when do they have speed cameras on the ILS?
As for the font, I'd recommend Fraktur
