Hold on thar...
The Holley spreadbore and the 4350 spreadbore are not compatible. The Holley is based on the Quadrajet design for primary and secondary bore spacing, which is quite different from the 4350. The 4350 does not share primary/secondary centerlines like the Holley or Quadrajet does, but rather has the primaries bored closer together in the carb base.

There is an adapter available, but sometimes hard to get, which would be one of the cheapest solutions but you are still gonna need another carb. If you can find a used 429 or 460 intake somewhere for sale that uses a square bore design, grab it, or get yourself an Edelbrock Performer intake and enjoy years of performance technology that is programmed into this nice intake manifold.

Here is the adapter from Summit: Part number TRD-2199
http://store.summitracing.com/partde...0&autoview=sku

Kinda pricey at $57.00, but will do the trick. Also works like a regular 1 inch carb spacer to improve low end torque. What I did was scrounge the junkyard until I found an OEM aluminum carb spacer that was made for a square bore. I then hand-machined the bottom of the bores to match my intake manifold, using an old gasket as a pattern. I just blended the ports smoothly and I got a great working setup that cost me all of $2 for the spacer and a little more money for a good used Edelbrock carb off ebay.