The 350 swap will get you familiar with swapping the engine. But before you do it read up on everything involved in the LS swap that way when you are doing the 350 swap you will be more familiar with parts and processes that will need done/changed/modified during the LS swap and should help in the planning for the LS swap. Look at how engine and transmission mounts, radiator, wiring, fuel lines(size, routing), trans linkage etc. are configured and installed. You want to do the same as you remove the engine from the van.