Boxer
It's much easier if I can answer via email. My email is
tomahawkperformance@gmail.com. I have the 5140 rods but don't carry pistons currently. The 455 with 6 x heads is a popular combo and works quite well. I can also get the right cam and good lifters for your combo. For a mild street combo cast pistons should be fine.
Tim Corcoran