I need some ideas on how to install this fan set up

Okay, the fan and shroud showed up today. The shroud doesn't fit the radiator so I had to drill new mounting holes. Then I had to drill holes to mount the fans. My problem is how I am going to mount the fan assembly to the radiator with the fans installed. The lip to mount on the radiator will be covered by the shroud and with the fans in place I can't reach through with a box wrench. he fans have to be in place because with the shroud mounted I have no way to get in to thread nuts onto the bolts. Here are some pics.

What I am thinking of is to cut a small notch in the side of the mounting bracket of the radiator. Just big enough to slide a nut in. I'll use a serrated lock washer, so with a 1/4 drive impact, the nut will grab and not spin. The trouble is, there is no room for error and I don't want to cut into the core.

Anyone got any good ideas? Please?

Here is the radiator. See the l shaped lip with the two mounting holes that is on either side. That is my problem, it is internal instead of being flanged out.
View attachment Radiator.jpg

Here are the fan assemblies laid in place and giving me headaches.
View attachment Fans and shroud ready to mount.jpg
View attachment Fans and shroud ready to mount 1.jpg