And the book sourced this to what? In Theory you could add a lot of bombs, whether you will be able to take off or not is another question. Maybe it's like the old myth for the Ju 87A and B - leave out the rear gunner and rear armament.
You could theorise allot of things...maybe this will work better for you?
from this book
So we have a D-1 the only thing Pyro has to do is rename it and add a siren. Which would be cool
Since the G-2 is the D-5... same as above just add 20mm instead of 37mm and add the bomb options.. name it D-5 also very cool
Two pretty simple things to do ... don't you think?