On 12/12/2019 16:42, R D S wrote:
It would be advantageous if I could connect up a rad with the flow and
return on the same side (top and bottom).

I get that best case scenario it will take longer to heat up, will it
take a lot longer? Will it fully heat up all?

I have my answer, about half of it heats up fine, half gradually not
diagonally but i'm not too surprised as it is wider than it is high.

I'm planning to connect a pipe to the feed that runs along the inside of
the bottom of the radiator, thus feeding at the opposite end.
I presume there'd be a benefit to a hole in that pipe near the feed end
and one in the middle (at least).