What is the difference in the 454 heads and the 496 heads? Will a 454 head bolt on a 496?

they are completely different heads and are not interchangeable.

Someone told me the water holes would not line up, but it sound like it is more then just that. I tried to look at some pics on line, but it was hard to tell.

GM 8.1L -496 Gen 7 hreads will not work on any older Gen 6 or earlier BBC engine .They have 18 head bolts per head versus 16 and they do not align. The coolant passages are not the same and these heads are not useable on a 454 or 502 engine block. Look for and buy yourself a good set of higher flow iron or aluminum cylinder heads for your engine from soemone like Dart or AFR, etc. Stay away from the cheap Chinese aluminum head sets being sold all over the internet and such!

Best Regards,
Ray @ Raylar