I have been thinking of doing the same in my 67 with a 351w. I am about 80% sure that the stock 5.8 intake is too tall, how much too tall I don't know, but it is too tall. Your other option is to buy aftermarket upper and lower intake manifolds for the 5.8. Only problem there is that they are VERY expensive, figure $500-$600 new for both intake manifolds. I am planning on using the stock lower intake and building a sheet metal upper intake that will fit under the hood.
I have done a lot of research on this EFI creation stuff, so if you have any questions send me an email or PM.