There is a WIDE variety of build specs for 427's, they were also used in dump trucks (boats, industrial motors for pump's, etc.)!
Seems to me most of the originals ran a 2X4 carb, could well have been a low riser in many or most cases. Comp cars and SC's were different. Of course plenty originals had a 428 as well. 12 second 1/4 mile was pretty common, nothing special really (VERY fast for that era though).
H.P. has been widely debated for a long time. I suspect many originals had relatively low h.p. Ford advertised 425 for their "big dog" 427 but for the most part I believe the side oilers easily exceeded that. The Ford Thunderbolt factory drag race cars were more like 500 right out of the box (high riser, 2X4, high compression, wild cam). The T-Bolts didn't stay "stock" for long though, you can be sure they were torn down and built up even more before hitting the 1/4 mile.
Some say there were more 428 Cobras than 427's, I don't know, it's hard to get an accurate number on that, maybe, maybe not.