Are you fairly certain on the c/r?? Sounds pretty good to me. I ran my 291 rect. heads (same size runners, but closed chambers) on my 454 several years ago..my cam was a little bigger, but I can assure you it was not a dog because of the heads...yes, they are a little on the big side, especially with the rest of your combo, but I think they should work out very nicely! You must have a domed piston if you're at 9.5/1, seeing as the 990's are supposed to be 118cc. I think I would just run it and dont worry. Yes, a gear change would compliment the heads, as would a converter and larger exhaust...but one thing at a time!! All that can come over time. Im still running my 291's on my current 505, and they are awesome. Good luck with it. John