Ok, so this is a two-part post.

First, would a 400sb be viable for my 85 z-28? It currently has a 350 from I think a 79 C10. It runs good right now, so I have time to properly build an engine.

Second, what kind of suspension upgrades would I need to swap in a 454? If I'm gonna do a swap, might as well go big. As long as it's in budget anyways.

 

BB swap isn't cheap. There are firewall clearance issues. I am not sure about steering or radiator fitment, but someone more knowledgeable might chime in. 400 will fit the same as your current 350 does....but beware the 400 head steam hole issues as well as flywheel balancing.

As far as suspension goes, I would recommend subframe connectors, new bushings, etc. and springs. The 400 sb with aluminum heads will be lighter than your 350 assuming iron heads,so keep that in mind. A bb will be heavier.

 

Take your 350 block and have it machined for a 383 stroker kit. It is a lot easer then finding a 400 that good and then you don't have the over heating problems eather. I would go one further and just do a vortec roller cam block. You can then use the roller lifter set up to go with a roller cam. You will not have problems with flat lobes because of the lack of additive is the newer oils. More power with a roller cam so its a win win all the way around.