I used the this
https://www.summitracing.com/parts/c...del/c10-pickup
The kit worked well, and included perches, slider mounts, DT tri y headers and trans crossmember. I have my 6.0L 4L80 setup as far back as the mounts would let me go and still have firewall clearance. The stock oil pan hangs down about 1/2" below the cross member. With the motor perches in the back holes of the cross member.