Jim, I got the pics you emailed me. I can't speak to the 461X heads as they aren't an accepted casting for my '68 327-275 combo. The book is a bit grey on the port volume...on one hand it appears that you can use the 461X @ 172 cc intake. On the other hand, it says the port volumes for heads are calculated on the 461X head when the 462's, 041, etc. are shown as 165 cc. And they all carry the same h.p. factor. Hmmmm...
While I sure wouldn't want to give up 5 cc's on the intake, the exhaust side is pretty important, also.
-Al