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).

aka plumbed TBSE, obviously the flow has to be the top, return from the
bottom, or the water will short-circuit it.

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 a radiator plumbed TBOE, rather than the usual BBOE, it warms up
fine.