70 c10 header, crossmember, lowering question

[DS3685]

Hi everyone. Im working on my 70 swb 2wd with a 350 and T5 in it with stock motor mounts with v8 towers and in the forward position. Ive been searching and reading until my head hurts about headers and what people are doing for fitment with trucks that are lowered 5.5/7 (which im planning on). My problem is i have a set i bought off ebay and they are too low for my plans but they also hit the motor mounts and wont go far enough toward the front of the engine to bolt on and it looks as if i were to get them to fit they would hit the crossmember where the original 4 speed bolted up. I happened to have chevelle headers laying around (68-72) and tried them and they also hit the stock tranny crossmember. Im kind of at a loss because its not a matter or small notching or grinding its like they dont fit at all..Im assuming everyone leaves that factory tranny crossmember in even thought it isnt used?? Any thoughts or help is appreciated. Thank you