Nice little boa.
You can split the cage but personally if you are ordering a cage from AP, might as well just order 2 and do a payment plan with them. Personally for me, I would order a T10 for the BP and at least a T10 for the boa. A forever home for the boa unless its a male will probably involve a T25. i have my adult females and male SD retic in T25s. My BP and dumerils are in T10s and my baby boas are in T8s.
They take like 3 months to ship and being Christmas, i bet it will be even longer. Took like 13 weeks for 3 T8s to ship, 14 weeks for 3 T10s to ship and exactly 12 weeks for 3 T25s to ship but that was because I was Razzing Ali on T8s being a quick ship item when it took 13 weeks lol.
But if i were you, and was starting from scratch and knowing what i know now, i would just save up or do a payment plan and start off with a T25 for the boa. Otherwise you will end up like me with extra cages laying around that beg to be filled.....thus why i have a snow or moon lined up in about 3 months or so for my extra T10 hahaha.