Yes, I would agree that right now, the high compression ratio of our IDI's are the limiting factor. Nobody makes a set of head gaskets that can hold any more than 15psi safely, unless you want to go custome which would be super expensive. And since we can only push 15 or so psi into our IDI's, that limits how much fuel we can push into them, and thats where the real power is....more fuel. Basically if one could just turn up the pump and it could completly burn all the fuel (ie no black smoke plus excessive EGT's) then there would be no need for a turbo. The turbo isnt what makes the power, the turbo is just adding air so you can turn up the pump, and burn more fuel because you have more air.
If you want to get some good power out of an IDI, then it will cost you. You will need to buy some lower compression pistons (heard somewhere Mahle will make you them), or stock pistons plus low compression connecting rods. If I were to do it, I would probably drop the CR down to about 19:1, but it never gets below the teens here for really cold temps, and I can live with going through starters yearly. Then I would say go through the heads and clean them up some. Next you would have to do your standard rebuild things, maybe a custom ground cam. Then you will need some good injectors, and a high performance pump (ie DPS or Moose pump). Along with all that, you will more than likely need a custom turbo setup, though you might be able to get a hypermax kit set up for you from factory so it can push some good air (if you can 25psi, but it depends on how much you drop the CR). And an intercooler. Also, I would probably try to get a set of custome head gaskets to hold the boost. It would be an expensive build, but I think you would be in the 300-350hp range.