[LS short box]

I've done a number of LS swaps over the years.
Wiring harness/ecm for the engine and trans. I've used Speartech and Howell. Both have provided great products and great tech support. I would never buy the cheap ebay harness/ecm's.
If your 67 still has the as delivered chassis wiring harness I would replace it. LS swap need really good grounds and 12 positive wiring.
On my LS swaps I try to hide as much wiring as possible.
On my 68 C10 LS6 swap I mounted the ECM and fuse block behind the glove box. I had to section the glove box a bit to make room. OB2 port on the heater box.
Some use truck FEA. I like 2002 Camaro FEA with an LS6 intake. Speed Engineering headers. I know they are made in China but they fit well and I can't afford $1200 for just headers.
Couple of pics.