Those fentons may be set up for the earlier 216/235 and may not bolt up to a later (like 55-62 intake manifold) so you will have to check to see if what you have will bolt up. Frankly, you may be better off converting a stock manifold just to retain the stock exhaust manifold function given you want to retain the stock I bbl carb set up. Just as an aside on the converting the stock exhaust manifold, I have done this conversion a couple of times. There are three approaches. The first and easiest is to simply install/weld an additional outlet. Years ago the parts houses use to sell the outlets (think jc whitney, gotha others). This is the quietest of the setups also. The nest is to split the manifold, and install a plate just inside one of the halves with a hole, 1 inch or so, in the middle, weld the halves back together, and add an outlet on the other half. This is a truer dual set up but a little more louder (a little more rappy really) then the stock set up with an outlet added. The third version is split the manifold and weld plates to each half, ground a little clearance between the halves and add an outlet to the half that needs one. This is a true dual set up and the loudest/rappiest of the versions.
