So I have an idea for non run of the mill radiator design.
Griffin Rad who has built custom radiators for me in the past, but will not build it according to my requirements according to the sales staff.
They have concern about flex from the wide width, no matter how I support it.
I can't get to an on-staff engineer (a problem solver IMO).
Ideally, I want a 3" core 36" to 48" wide 12" H Alum cross flow plus end water tanks.
They will not even do a vertical flow this wide,, which is mostly a deal breaker for me because of extra height
Anybody seen/know of a cross flow Rad this wide?
Griffin suggests I use two radiators, which is unwanted.
Suggestions?

Try telling them 12" W x 36-48-whatever H, top & bottom tanks, then modify whichever tank you need to accept a filler neck.
Or, no filler, just in & out (2 bottom tanks), and the fill is handled separately.

Griffin, who I consider one of the leaders in the field will not build anything over 30" W period.

There is an early Cherokee radiator that is horizontal 36x12, which another company offers, but its only rated for up to 400hp.
I'm shooting for 500hp, and wondering if maybe E85 and a large oil cooler will get me where I need to be.
I'd rather not be on the edge cooling wise with a Florida car.

Alcohol engines run cooler than gas engines; heck, we'd let the Sprint car - no radiator - idle and/or forever just to get it to 160 (iron block & heads).
You could also isolate ATF cooling if you have an AT.

A wider than normal radiator that isn't very tall going to hold enough volume of fluid?

Radiators - https://youtu.be/OxnFR1Fc-Jk?si=Dk2qQUJqL-QUo6Vz

Fans- https://youtu.be/RcmZUYjEtCI?si=wDjIvtg0pj_Vra3M

Water pumps - https://youtu.be/dRuSkb2FIX8?si=r5IvRjokpdSRz_-6

Give Ron Davis a call. I've used their rad/shroud/fan package to cool a screw blown HEMI at 1622hp and an N/A W8 small block at 898hp. Both on gasoline and both street driven.