There's a question at the bottom of this post.

I'm short on pictures at the moment. I've also never owned an original 455 car so I'm also short on examples re: how things are supposed to look. I am moving all the hoo-hahs from the top of the stock '77 403 to the top of the Performer-RPM intaked' 455.

Some things are not fitting because of the difference in size between small block and big block - like, for example, the line that supplies vacuum to the brake booster. It's designed to bolt to a valve cover bracket near the booster - however, because the BB is wider, the bend on the tube is in the wrong place (too close to centerline), and the tube won't reach the bracket.

I need to either modify the 403 part to fit (difficult) or procure the correct 455 part.

The '77 Pace Car with 403 unit threads into the lower rear of the carburetor. It's function is identical to the 455 part shown below AND the part below looks very similar (perhaps slightly bigger) - HOWEVER the part shown below specifies getting vacuum via an _intake_manifold_ fitting_. It does not say that the fitting screws into the same place on the bottom rear of the carb as the part that came off the 403.

http://www.supercarsunlimited.com/Bo...Kit-d2646.aspx

The OPGI part similarly specifies that it "...runs from the intake manifold".

https://www.opgi.com/cutlass/C240531/

Do these 455-spec parts actually screw into the carb base the same way the 403-spec part does?

 

No, both those parts are basically the same and screw into a vacuum port in the manifold.

 

Here's a picture of the 77 403 booster line as it was installed in the 77 Pace Car. You can (hopefully) see how the threaded end mates to the rear bottom of the carb:


There is a manifold vacuum port very near that location - however, it is supplying vacuum to the HVAC controls.

So the 455 big block booster line doesn't get its vacuum from the same place (the bottom rear of the carb housing) as the 403 small block?

 

First, the BBO was never installed in the 1977-up B/C body cars, so there is no "factory correct" tube. Second, the location of the vacuum tap for the power brake booster DOESN'T MATTER. Most older Oldsmobiles (big and small block) used a tap from an intake runner, not the carb. So long as you are using manifold vacuum the booster neither knows nor cares where the connection is made. Heck, my 67 Delta simply uses a barb elbow in one of the rear intake runners and a hose to the booster. Later cars used an NPT to IFF 90 deg fitting and a metal line to the hose.




Supercars sells a version of the 1969-72 parts.

 

I am very much aware that BBO was never offered in the platform I'm working with - that's what makes it so _Exciting_. I also understand that vacuum is vacuum no matter where it comes from.

I am endeavoring to make the BBO look as stock as possible in this '77 engine bay - that meant retaining the valve cover bracket that holds the booster line, for example (instead of just going with flex hose all the way).

I was hoping to use either the 403 factory booster line piece, or the factory 455 piece - but I was unaware that the method of drawing vacuum had changed in the intervening 10 years.

 

The wider intake on the 455 means that when you attach that current line to the base of the carb, it won't line up with the bracket on the valve cover. Just bend a new line. There's no magic to this.