I love 273's but the rpm level with ported Speedmaster heads would be added valve train cost and pretty much put one in a race engine category. Custom Pistons are not that much more expensive, I've paid less than $800 and you get exactly what you want. Custom pistons are not needed on a 273, stock 2 barrel pistons are "0" deck and yield a little over 9:1 compression with uncut 64-67 heads.