The KB167 pistons are a great deal.

https://www.uempistons.com/index.php?mai...products_id=521

They're not cheap, around $300 plus shipping if you shop.

That link gives you the comp ratios for different head volumes. But my calculations show that those numbers are for a later block with deck height 9.577

On a 9.600" block, what you have, the piston is 0.012" in the hole. With a Mr Gasket thin head gasket you have the perfect 0.040" squish clearance if you use a closed chamber head.
There is no earthly reason for the first overbore to be 0.030, it could as easily be 0.020 and leave you meat for another rebuild later. 393 x 3.31 = 321 which makes 658.2 cc swept volume. Valve notches are 5cc, I'm assuming the head gasket and the volume from the 0.012 below deck as 9cc.Thus there is a total of 73 + 5 + 9 = 87cc.(658.2 + 87) / 87 = 8.57:1.

Put on a 63cc head and it turns into 9.55:1. Hello 262 cam (218/224 @ 50 lift).

Of course put a 4" crank in it, it becomes a horse of a different color and then your J heads will have some cubic inches to play with. But you have to decide.

R.