Piston to valve clearance. The x cam has a .542 lift both of my buds had to have their piston fly cut for clearance. Stock ported heads with 1.90int 1.60 exh. Chances are you will have the same issues.
The problem is not the heads is the clearance between the the valves and stock pistons. You really don't wont a piston to smack into a valve. If that happends one of two things will happen. One you bend a valve, Or two you punch a hole in your piston.
Lift is not such as concern as duration is. All the tolerances stack up: timing chain, production tolerances in the pistons, head gasket thickness. It's best to just clay the pistons and find out.
If your gonna swap out that pathetic B cam, why not put something in thats will work with what you have? Seems like the anderson B25 cams works great with those heads. A dude on corral made 299hp and great tq and under the curve with a combo just like you, un touched P heads and a street intake. hate to admit it, but the car made what I do and what majority of afr/fti guys make but with a cheap $300 iron head. It ran the # at the track too, high 7's @ 87 if I remember correctly.