It isnt the matter of using the 1262 or the 1250.. the restriction is between the pushrod "dimples" and no matter HOW big the opening is... it will only open up so far between those places... keep the 1250 .. they are really better balanced to the amount you can remove from the pudhrod dimples... cool?? and your rocking!! IF the intake is already at the 1262's... then do it, and the flow will still be smooth instead of hitting the edge of the intake port on the head...cool??
believe me or not its pretty good you can put it on a stock casting and use a permanet marker to color on the inside of the gasket and then port that baby out!!
I'm with thumper. opening up the entry will not help the flow. fact will probably reduce the flow. I always just true up the head port with minimal amount of removal then match the intake side to that.