I assume you're talking about all the various tubes you need to bend, etc.
The ones that are behind the baggage bulkhead, you won't be able to install. But you can still make them now.
When I did my engine kit, I found that the tubes were fit very well.. and only only of them I needed to wrangle a little bit (just bending it by hand in a spot was sufficient).
Also, make sure that Section in your KAI is up-to-date.. they changed a couple of the tube bends recently (July 28 2018)