G&p woc & bomber front set

[gotchya24]

hey there
lookin for some help with this..

the upper receiver im talking about is this one:
Bomber VIS-1 Carbine Length Upper Receiver For WA M4 Series
http://www.airsoftglobal.com/product...ducts_id=11388

im trying to get a different upper to go with a G&P woc..on the site it says for WA m4 series, it also says special design to use with prime too..i tried to fit it with a g&p lower, but the rear body pin on the upper wont go down because the rear end of the upper (stock tube end) wont go down..its likely gonna need some sanding etc...

anyone know if this is gonna work at all??? or what parts i have to modify so that everything works?? ANY help would be great...
over at GGI forum the 2 ppl with this upper have prime lowers...but i havea G&p so im kinda stuck..

thanks in advance!