I had thought that a 738 would be pushing its luck a bit too far on that one, particularly the return with not too much runway to get off from, but needed reassurance !
The 757 is definately best for this route, but, some other TUI Airlines use their 738s to the Cape Verde Islands non-stop with a similar distance as from GLA.
Try book extra space seats if you're tall though as the space for such a long flight, especially on the ex-FCA a/c can be tight. (ex-TOM have Slimmer seats with more knee space as you probably know?)