throttle bore presents no problem, for it is the same on the intake, the Holley 4160 (600CFM), and the Autolite 4300A (600CFM): 1-9/16".
The main concern is the difference on the secondaries, for the secondary throttle bore of the intake is 1-11/16" (to match the 4300A), while the Holley has the same 1-9/16" throttle bores - a 3/16" difference. It's such a mild spreadbore that most people mistake them for squarebores without bothering to look close enough.
To my knowledge, no adapter exists. If the 3/16" difference matters that much to you, you are pretty much stuck swapping the intake to one with 1-9/16" bores throughout.
That said, I chose to mount my 4160 directly onto my '71s existing manifold. I'm not too concerned about the fit - the whole carb has about half a millimeter of play on the shafts, and the factory boring of the manifold is pretty crude to begin with.
You might wish to look at my thread on the same subject: http://www.7173mustangs.com/thread-carb-...51c?page=2
(10-01-2012 10:42 AM)comanchepilot44 Wrote: I have a trans-dapt carb adapter (2199) off my spead-bore manifold. Spread-bore to square-bore. It worked great but I changed to the air gap manifold and no longer need it. Let me know if you're interested in it. $25.00 + shipping.
That adapter won't work for him - that adapter is for 4300D
spreadbore intakes with 2" secondaries. Those were used on the '72/73 4BBL intakes only (and later Ford intakes paired with the 4300D or 4350).