Listen to Moobs Dan. Use the number he gives you, he's done a ton of saws and has more hands on experience than all of us.
Don't widen the uppers. Slows velocity and you can catch a ring.
There's a fat fin over the roof of the uppers externally, so you shouldn't be able to cut through the roof easily. Try to enter the chamber flatter on the exhaust side and more angled on the intake side of the upper. Slope it upwards as you move towards the intake.
No fingers Dan.
The flywheel side tunnel has a lip in it-you'll see it. Blend it internally but don't cut through.
With the bigger carb, that low intake duration should work fine. I'd probably stay more like 122 on the uppers, unless you lower the intake.
Realize that when fingers and bridges are added, case volume increases and pressure drops, so you need more transfer duration.
The 262 jug is an excellent foundation for serious perfomance mods.