looking into swapping a 454 in to my 89 will the stock 454 manifolds fit?I have done a search on this site as well as others but can't find any info.I don't want to go with headers I have a rough driveway and would end up smashing them anyway.has anyone done this swap and tried the stock exhaust manifolds.if so what was the manifolds off of.I have some but they come off a truck and it looks like they will hit the firewall on the right side.

 

A custom y-pipe may need to be fabricated but stock cast exhaust manifolds will be the best fitting manifolds you can use. They also offer the worst performance potential being very restrictive. They'll also reduce underhood noise better than any headers.

For a low buck swap, use the factory manifolds.

 

It depends on what manifolds they are. Some may fit, others CERTAINLY will not. Truck ones in particular are not likely to work. Chevelle or Camaro ones might.

Given that about 99.99% of all stock manifolds you'll find just stuck on some 454 core you're going to just up and buy, will be truck ones, I'd put pretty good odds on them not fitting.

You'll also find that because of the arrangement of the head ports and the angle they sit at, big block headers in general are MUCH MUCH better about ground clearance than small block ones.