diferent length s/c to tb pipes = different flow characteristics between the pipes
basicly just like cabrbed v8’s with dual plane manifolds, that setup has dual plane intake pipes so to speak
this could lead to him having trouble keeping all 6 cylinders @ the proper a/f ratio at all times … 3 could be to a lil to lean while 3 are slightly to rich
the pipe off the s/c should probably come off the SC horizontal, turn straight up@ the middle of the engine, then split into a pair of mirror image pipes that head off to the TB’s
but thats just me and my opinion …