IMHO< the problem is you are using a set of car headers in a truck chassis. a few members have done this in the past and posted pics and has be discussed many times.

my experience swapping in B/RB engines into 72-87 trucks is ONLY B-BODY headers required the top frame rail trimmed for clearance. and depending on the B-body header brand they can be shaped differently and require more mods to work. plus plug wire routing is a PITA. and they tend to hang lower than the frame rails which can be a problem on a lower truck or 4x4. 4x4 definitely needs room for the front drive shaft which B-body headers do not give.

a few other facts I have found with the trucks headers are 2x and 4x4 are different but there are some that will fit both.

on my 85 318/727 I had a set of hedman 79080 2x headers. fit great BUT only a low torque stock starter fit and needs removed to R&R it. BUT.. a mini starter can be R&R with out removing the header.

then when I installed the 2x NV4500 5 speed and hydro clutch from a 93 truck. I found #7 tube in the way of mounting any starter so they are a no go with a hydro clutch NV4500 bell housing. (the 833OD 4 speed hydro bell works ok)

so for the NV4500 hydro bell I needed to use a set of hedman 79170 (IIRC) 92-93 4x4 (magnum 5.2/NV4500) #7 tube differ and fit only a mini starter which was stock on a magnum 5.2 truck.

also...same deal on trimming frame rail with SB A & B-body headers in trucks.

it is the header not the frame.

79250 are the best fitting 2x or 4x4 for the $