The top of my rad ended up much lower than the top of the engine on my Sammio build, which is why i opted for the separate header tank fitted on the bulkhead, plumbed in where the coolant would have normally have gone to the heater matrix.
A few of us at the time (i think Trev and Pat also) all went for Renault Megane units as they were easy to mount, quite compact and can be picked up for pence, but this time around I've got an alloy one left over from the Lambo cooling fiasco.
I managed to dig up this pic of the setup on my old Sammio in case it's of use/interest (i know it's not exactly the same as what you've got and what you're doing, but i can't imagine it's too far off?)
It shows how low my rad ended up and exactly how much over-spray i managed to accumulate while sorting out the bonnet edge
Worked a treat