I have noticed that a lot of the newer 4150 style carbs are coming through with an elongated bolt pattern so that they fit either a 4150 or 4500 intake without an adapter. Does anyone know offhand if an older 4150 base plate can be modified in the same manner?

I was looking at doing that recently. It looks like the standard 4150 plate will be fairly thin around the bolt holes if modified in that manner. Not saying it couldn't be done because I think it could. It's probably not worth it unless you have your own mill and can do it yourself.

I ran into that when adding a 4150 throttle stop to a 4500 intake. I normally use a 2" adapter but couldn't fit the 2" throttle stop under the hood with the adapter. I actually made a 1/2" plate aluminum adapter. It worked great. Pictures are on my FB page @mwracingcamaro if you're interested.

This is a 4150 Edelbrock SV2. Like has been mentioned it was thin so we added material and ground smooth. We had one with no material added as well. It's on a car over a year, seems fine haven't gotten any complaint.

Mike do you have a picture of the 475 lb. added weight? How mounted .

Cheaper to buy a bare billet baseplate from BLP and swap your shafts and blades over. You will need a plate to go under it to cover the sides or otherwise you will have a vacuum leak, and to make sure the linkage clears the manifold. I had to make a custom plate for this.