I am a huge fan of Edelbrock.  they flow rally well and produce lots of low end torque.  An OEM type unit is not going to flow as well as any of the various aftermarket options even the less popular but less expensive brands AND most OEM units are cast iron so the weight savings with an aftermarket is substantial.  The other issue is cost.  Most of the OEM units are being run by purists and those for sale will be close if not more expensive  than an aftermarket unit.  Thats my two cents on it 

it is not that simple.  every part in an engine as a range of power it can add, but where in that range depends on the other parts.  What is the compression of your engine, are you running headers or stock exhaust manifolds, and is it a stock cam?  I am assuming you are running the stock cast iron heads.

A 1969 351 4 barrel had 10.7 compression ratio, the 2 barrel only had 9.5. So your HP gain would be a little lower than the 40 HP.  

The heads for the 2-barrel and 4-barrel cars should be the same.  The difference in compression comes from the shape of the pistons.  There are three things causing the "flat spot" you speak of:  the intake/carb, the exhaust, and the cam shaft.  The best way to think of an engine is like an air pump, you have air flowing in, air flowing out, and valves in the middle to time everything.  IF you improve one of these three things you will see performances gains but you will see bigger performance gains in conjunction with the other two.  Headers are IMHO the single best bang for your buck.  By eliminating the restriction of stock exhaust manifolds AND adding improved scavenge you will typically gain 10%- 15% more power.  Adding a 4-barrel intake and carb will add power especially at the upper RPMS.  Think of it like this if you tried to breath through a pipe it would be easy, but breathing through a straw it would be hard to get enough air and would be more work.  Same thing applies to a good intake and carb.  When its easy for the engine to suck all the air/fuel it wants/needs into the cylinders than than each detonation will be max power and less HP is used sucking in air so thats now HP that goes to the wheels.  40 horses for your setup is probably on the high side, but the 30 HP you could probably pick up would be well upgrading the intake and carb  AND if you added a set of headers with the intake you could probably pick up 50 or 60 HP total between the two.

The third thing being the cam shaft (which controls your valves) is where the compromise between low end torque and over all HP happens.  I prefer to run a mild came with lots of low end torque and then I do everything I can to make the engine breathe well and I end up with the best of both worlds.

Hi Sanddoc, thanks for the information, much appreciated.  The 351W is in good running condition and I'm not a hot rodder, so am not on a path to plunk a bigger engine in the barge or make significant power adding modifications which would stress the rest of the drive train.  I like getting as much as I can from a motor by freeing it up with better air induction, upgraded ignition system, and better exhaust.  One thing I did to that was in your post was to convert to the Pertronix and as well added an MSD spark box for good measure.

The EFI modification would be fantastic, just a little pricey for me right now.  I also have a '64 TBird 390 car that would probably be first up for an EFI upgrade.  For now, carburetors are my friend now that I'm remembering how to tune the darned things.

The Galaxie is actually my wife's car, belonged to her parents and has been in the family since 1974.  So I don't want to change the overall appearance and ambience of the car, but what she doesn't know (like mild power adders) won't hurt her, right?

I think maybe the next move will be headers, then we'll see where we go from there.

Thanks!

Doug