Stock 351W heads suck. 1969 was the best year for them if you do end up using them. But I wouldn't recommend it. Maybe if you did a really, really nice porting/polishing job on them they would be halfway decent. But, it'd be much easier to go with aftermarket heads. They make iron heads if he wants something kind of close to stock, or just get some nice aluminum heads like the Edelbrock RPMs.
Easiest way to get 400 hp with a 351W. Edelbrock Performer RPM "Power Package". Heads, cam, intake, 750 carb. Check out their website. They tell you everything you need to know.
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Previously "BennyBoy"
'69 Coupe with 351W-I rolled it 8/8
Edelbrock RPM intake, Edelbrock RPM cam, Edelbrock 750 cfm carb, Hedman headers, 2 1/2" pipe, glasspacks, C4: shift kit, 9" Currie: Trac-Lok 3.70s, 290hp-stock heads