Sure the p-47 could have carried 6 x Hispano's, especially M3's.
The .50 BMG weighed about 30 KG, the Hispano II (or AN-M2) about 50 KG, and the Hispano V (M3) about 42 KG. So eight .50's weighed about 240 KG, 6 x AN-M2's about 300 KG, and 6 x M3's about 252 KG. There would be room for at least 200 rpg.
In actuality, they were considering a P-47 with 6 x 37mm guns on it, and the M10 37mm weighed a wopping 96 KG each, so 6 x 20mm's was certainly doable.
The 20mm would probably have been a good idea, but remember the Hs.II had almost 3 times the rate of unclearable stoppages as the .50 BMG. Also, all sides had problems with cannon freezing at moderate altitude (above 15-20K). This was especially a problem with the Hispano which fired from an open bolt - allowing cold air to rush through the barrel when it was not firing. On the F4U-1c, guns would almost always freeze above 15,000 feet, despite the presence of electric gun heaters. Spitfires had problems with the Hs.II's freezing at altitude too.
=S=
Lunatic