[Putt]

After 1977 the 351W used the same valve size as the 302 so those later years, the most common, won't help at all.
The bump in the exhaust port is for the AIR(smog pump) system, it is either drilled or un-drilled, but it's purpose is not flow restriction for a "sniffer". It does cause a flow restriction however.
Backpressure is not going to help with low end torque, a free flowing exhaust will help with both low RPM and high RPM power.

By the time you buy a set of '69 351W heads, install hard exhaust seats, new valves, valve guides, stem seals, springs, retainers, keepers, convert to screw in studs and guide plates, you could have easily bought a set of World Products cast iron Windsor or Windsor Jr. heads with all that on them AND a much better chamber design AND better port flow.
For a little more $$ you could buy some aluminum heads from a number of manufacturers.

 

[Putt]

If you can get that good of a buy on the machine work and parts, go for it. Summit has assembled Windsor heads for $409.88 each, they come with 2.02, 1.6 valves,64cc chambers HD retainers, locks, hp seals, screw in studs and guideplates for 5/16" pushrods.

I am not disagreeing on the 351W heads being adequate for a mild street motor, I just have not seen very many '69 351W heads for sale. Since the Windsor(World Products) heads come completely assembled with good parts, there is no extra cost once you get them and they will FAR outflow the stock heads, even with some porting.

 

[Putt]

The parts to finish a bare set of early 351W heads with stainless valves(2.02 or 1.94 and 1.5 or 1.6), steel retainers, springs, valve locks, valve stem seals, screw in rocker studs, and guideplates from Summit Racing(there may be better prices, they were easy to get pricing from) are $330. If you buy the 351W heads for $200, you have $530 in PARTS. If you can port, tap for the rocker arm studs, mill for the guideplates, replace the valve guides(about $1.00 to $1.50 each), install hardened exhaust seats(the seats are usually about $1.50-$2.00 each), mill the head surface and perform a good three angle valve job for less than $300.....I want to know who you have doing the work!!!! :happyhapp

I know in this area a basic valve job with a couple of new valves costs that much without any performance extras. :handball:

I am not arguing that the 351W heads won't work, I just think it is cheaper to buy completely assembled performance heads for any Windsor style engine. IF you are contemplating adding performance components to your engine.

The Windsor Jr. heads have 1.94 and 1.6 valves, but I see they are $469.50 each and have 58cc chambers. I was incorrect on that price. :dunce:

 

[Putt]

Good point, Cracker, I had forgotten about those. I think you need to be careful which GT40 version you get, so the exhaust will fit from an early Mustang.