Installing a Wiring Harness - 47 Coupe

[Clrascoe]

I am replacing the wiring harness on my 47 Coupe. The dash is currently out of the car. I would like to install the new harness to the dash while the dash is out of the car and on a workbench but I am concerned about getting the other half of the harness (the engine compartment wires) through the hole in the firewall because the section of the harness where the engine compartment wires split out, which will need to go through the firewall, is so thick. Does anyone have experience with this issue? Thanks