410'

I would also buy new RHS heads before spending $1000 on old iron. Not that they aren't good. It's just the new RHS heads with just a mild p&p will be better and with a decent roller cam should easily get you to 500 hp. Actually if you think of it you can put $1000 into a set of X heads or buy a new set of ready to go RHS heads from Brian @ Indio Motor for $1300-ish and sell your old X heads for $200-300 and the money is real close to the same but you end up with better heads.

4:10 gears are fine race gears but not very street friendly gears IMO. I had them in my Cuda with a 27" tire and it was screamin down the hwy at 60 mph. 4:10's might make it a little faster than 3.55's or 3:73's but they don't even compare in driver friendly-ness of the takker gears. For what it's worth I took the 4:10's out of my car and put in 3:73's and it only lost a tenth in the 1/4. Dropped the 60 mph rpm from 3450 to 3000. I wanted less rpm yet so I put in 3:55's and it dropped the rpm at 60 to 2800. Lost another tenth but it was worth it since the wife and I like to cruise a lot. Gained 5 mpg too which sure helps when you have to run premium.

One more thing. I would think .040 over would be ok but I'd have the block sonic checked just to make sure there isn't a thin spot(s).