The "512" kit (really 505" at .030 over with a 4.25 stroke) is really nice in that it drops into the block when you use the 2.20 Chevy rod journal. The closest point is the oil pump pickup boss. Usually okay with ~.060 clearance.
Not sure you need the extra cubes because all you are doing is moving the peak numbers the heads produce lower in the RPM range. You will have GOBS of torque with the 512. Mine makes 714 ft/lbs. At 3450 RPM with head numbers similar to the Trickflows.
Mine has a small hydraulic roller and it pulls hard to the 6400 rpm limiter.
To be clear, with 4.25 inch stroke and 0.030 inch overbore it works out to a 505 cubic inch. 0.060 inch overbore will equal to a 512 cubic inch motor.
