Greetings - I had Stein build my panel and had the same situation.
My suggestion is to remove the connectors that have to penetrate the spar and the fuse sides. Also, be sure you have a good routing down the firewall. I routed mine all in two bundles along the sides of the heater box. I ran the wires that went to the aft fuse down the left side all the way back to the servo.
Before you start, plan your routings (ALL!!!) and where they will penetrate the spar. I think you will have plenty of area for all these wires. I had my snap bushings loose in the holes and they would come out when routing. I used E9000 (like ShoeGoo) and glued them in place. If yours are loose, do this before pulling wires.
I caution you on the transition from the firewall to the floor - be sure you make a kind of fence so that the wire bend is tucked tight into the corner, otherwise you may have to cut the tunnel cover for the wire bends.
I split the corrugated wire tubing and covered each bundle from 4-5" above the floor on the front, back to behind the fuel pump (I have an IO-360).
You will have to decide which end gets terminated first, and since Stein has started for you that means the panel end. Then as all wires are run, you can make nice tight bundles beginning at the panel then progress to the end as you work your way back in the fuse. This will allow you a smooth look and easy routing corrections.
You may have extra wire in the stein bundles at the ends, use a loop to take some slack then cut and re-terminate as needed to make the ends neat. Get some solder sleeves from stein and extra green and black wire for grounds as you re terminate.
YMMV, but having done this same thing, this process will avoid some headaches that I had.
Good luck, Let me know if you have questions, I can send pictures too of specific areas.
oh - I used 100's of the white zip ties in the bundling process (put on cut off often) , and finally used black Thomas&Betts ties (all weather, UV resistant, metal tang) for the final tie downs and black lacing for tying the bundles. I like the clean, light look of the lacing better than the zip ties.
