Rear Shock length

Hey guys, I have searched the forums and read alot of posts, but still feel like my questions haven't been answered. I am upgrading the suspension on my 04 D-cab. Currently I have Monroe Reflex truck shocks with the factory TRD springs and a 1 inch spacer on the front and Monroe Sens-a-Track shocks with a 1 inch block under the rear leaf springs. I will be putting Toytec coilovers on the front. I plan on scrapping the current rear leafs (factory) and blocks, and getting the Alcan 5-leaf springs for the rear. I haven't figured what height I want to set the Toytecs at yet, but I know the Alcans will raise the back end approximately 1 to 1.5 inches. Ideally most would say to get new Bilsteins to go with the new springs, but I don't have very many miles on the rear shocks I currently have. If they could handle the extra lift, I would like to keep them on the truck. The big question is what length do my shocks need to be to handle the lift from the 5 leaf alcans?

Thanks