That is a big step forward. If it was me I'd do a 4.50 x 4.25 with 7.10 long rods. You'll most likely need to buy custom pistons to get the compression correct for your application. The TF270 heads will work great with 540 cubic inches.
You could go 4.500 but then the internal oiling starts to get tricky. Typically a 4.250 stroke with 2.200 rod journals will clear normal street pans, pickups and windage trays.