It only needs to tilt as far as it needs for clearance to the nose, not necessarily to fit the same OAH. Any space left between the rad and the nose tops, sides and bottom will have to be shrouded for best cooling anyway. My Civic rad fits in a std Kinetics nose while tilted a bit (~15 deg+/_ ?) but nowhere near that 48 deg. I see you are using a different nose. That will certainly determine what is needed. Supposedly, the Stalker's Hyundai rad is lower and wider than the Civic and would not be a "custom build". They are reportedly cooling 3.8L superchargerd engines on the track with that rad. It may be an alternative. You'd need to do some research there to find the correct model.
Core area of your Caterham drawing = 163 in sq. (Not sure of the core thickness. It may be 2"+)
Core area of the Civic radiator= 194 in sq. (tpically, the dual row 2" Civic radiators have 13.78 x 14.09 x 1.65" thick cores.)
The Caterham uses a 11" fan. You can get a 14" fan to fit nicely on the Civic rad (smaller on the stalker). Not knowing specific fan models, I just compared two same-make same-model fan data for the 2 sizes. The 11" was rated at 1075CFM the 14" was 1769 CFM, or 64% more. There are better fans out there and the ratings were just in free air, not a real test condition mounted to a radiator. But it shows the relative advantages between the 2 sizes.
From a fan point of view the Civic rad w/14 inch fan would be much better in traffic or on the grid. From a core area point of view, hands down again to the Civic. As for core thickness, the Caterham has the upper hand. Real world???? Most of us don't swap out radiators just for a test so I doubt you'll have any real data to know which will be better in your application.
I hope this helps to make some informed guesses.