Mount side pipes before body goes on?

[FRM]

So I'm dang close to a first start. Headers arrived this morning so mount those and the J pipes do the priming, add fluids, etc. and I'm going to try to start it. Question is........mount the side pipes before the body is on, or do some kind of temporary side pipe support set up until I put on the body and have that to measure to.

What do you all think? Thanks. Is a 289 with a 302 by the way

Fred