Don't buy pistons until you know what heads you are going to use and the chamber volume. Once you know the heads, you can coordinate the piston crown configuration and the chamber volume to finalize your static compression ratio. Then and only then, you can begin to look for the proper cam.

You will want to be on top of the squish also as you do your planning. With the small bore, you can hold the squish at or near 0.035" to 0.040". If you stay at or below 9.5:1, you can use a fairly tame cam for good manifold vacuum and good low-end response. With tight squish, the motor will not detonate at 9.5 with iron heads on pump gas.