[Cuccos19]

"The B-29A was powered by four R-3350-57 engines. 1119 B-29As were built, block numbers reaching -75. The 20-mm cannon was removed from the tail turret beginning with production Block 20, and a pair of 0.50-inch guns were added to the top forward turret to provide additional protection against fighter attacks coming from the front."

That was the actaul site, unfortunatelly it's out of service now. I find the infos on my HDD in saved htmls.
http://www.csd.uwo.ca/tips/elevon.is.go ... b029i.html