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The 351W has a taller deck height(about 1") so it will be wider than a 289/302. It will still fit but you will need to get special headers to clear the shock towers.

 

And, what spedial headers do we need to get in order to put a 351W Into a 65-66 bay? And what do the shok towers have to do with the headers since the headers go underneath the shock towers. I think the main concern is the starter motor clearance.

 

The taller deck height pushes the heads closer to the shock towers therefore you need headers that won't hit them.

 

if your trying to go big, basically the biggest thing you could easily fit would be a 347 stroker, since it utilizes a 302 block

 

351W with the 351-65/66 swap headers fit, but they are TIGHT! It'll be a PIA to change spark plugs. A 302/331/347 with a blower would make monster power and still fit well. If you wanna be really classic looking, stick a 302/stroker in it with like 7.5:1 or 8.0:1 compression, and a Weiand 174 Powercharger roots style blower. It's a short height blower, and will fit under the stock hood with the right air cleaner. Though, roots blowers have crap for efficiency, but that's another matter entirely. It'd be a potent 302 that's simple, looks classic and drivers nice