Permaseal also make spacers, or "head saver shims" as they call them. They're actually intended for use when the head has had the bejesus machined out of it, and the CR has gone too high. I believe they are available in .75, and 1.5mm.
The upside for folk like us is, we can lower our CR's without a full motor teardown.
Have you ever lowered the CR of any of your motors? Too high a CR will be the kiss of death for a forced motor.
HOWEVER, the bloke who does my boring/honing etc has advised me that too low a deck height, can actually promote detonation!

I read a thread ages ago at a mopar site, where they were discussing minimum piston to head clearance. The general consensus was that the tighter the squish, (And therefore the higher the CR) the less likely a motor was to ping.
Of coarse a forced motor is a bit different.
If I could afford forgies I'd run them at zero deck, with a nice dished out bowl to keep the CR down. Take a look at datsun100A racer's photo of the pistons he hand machined out so the dish was offset to be under a closed chamber head.
On my latest engine I increased the dish in my pistons,( larger diameter dish, not alot deeper. And still kept the squish band around the periphery) and used a head saver shim. I never actually measured my CR, but the static comp is around 130psi.
As far as I can tell, (The zhorst is a bit loud) I don't have any detonation.
If you're building a new motor, I'd dish the pistons, and O-ring the block.