Wallace uses rear wheel hp. Compare these two, they use the same formula.
http://robrobinette.com/et.htm
http://www.wallaceracing.com/et-hp-mph.php
The Hemi lx cars don't fit the formula.
You can use the formula to compare your power to the ground vs an lx power to the ground, but realize the output 'hp' numbers probably aren't correct. Also, given you have a different tranny, it's not going to be a spot on comparison (lx's have more gears, thus tighter rpm band used, though probably more driveline loss).
if you're looking at trap speed, then drivetrain loss always matters.