My initial impression was that Bell only operated 20' and 40' containers. However, a bit of research has shown that Bell were actually innovators in the whole intermodal area, and are still regarded as such, with patents being lodged for pallet wide container designs and were also one of the first intermodal companies campaigning for the EU to allow the use of 45' containers, so they came up with a specific design of 45' container corner edges to beat the EU legislation then in force. In fact, their patents were later sold onto Cronos, who still use them, amongst others.
So far, I have come across evidence that Bell operated 20' tanktainers, 30' bulktainers and 45' containers. However, while the 20' and 40' containers were the most common on Bell liner trains, there was occasionally 20' tanktainers and 30' bulktainers used on these trains too. I don't think that the 45' container was ever used on Bell liner trains though, or at least yet to find evidence of that.