I beleive an assessment of the Orion was made at the time of OR.381, but range/speed etc ruled it out. There was also a Trident variant (HS800) that reached the final candidates.
There were a host of proposals based on airliners that were considered as part of the overall process leading up to that point - a Comet version was first proposed for OR350/MR218, and over the 50/early 60s Brittania and VC10 variants proposed, as well as new build aricraft designs like the Acvro 745 (which looke dlike a cross bewteen a Shackleton fuselage and an Andover wing!)