Engine/Transmission (1998.5 - 2002) I need an ecm for a 2002, which one should i get?

[peplepew]

I recently picked up a 24v out of a rolled Ram and plan on shoe-horning it in my motor home. The problem I'm facing now (and I'm sure there will be many more later) is that the engine came without an ecm. I plan on doing some bombing, and I'm wondering what I should do about an ecm to start with. I plan on running a beefed up automatic transmission possibly an Allison. The motor came out of a truck with an automatic. Should I buy a new or used ecm. Should I get one for an automatic or manual. Any advice would be greatly appreciated, thanks!