LT1's and turbo's
Don't worry about o-ringing the block unless you are looking for large (+1000, etc.) hp levels. At lower hp levels you don't need to hold normal cylinder pressure, so the only time they will come into play is when you detonate - this means breaking a piston probably vs. just a headgasted.
Cam - heavily depends on the rest of the setup (primarily turbo choice and motor displacement, as well as intended boost).
Boost levels - depends on how much horsepower you want to make.
Honestly if I was doing this in a 69 camaro I wouldn't bother with the LT1. Go with a nice aftermarket 400SBC style block (say like a dart iron eagle) - *MUCH* stouter block to work with, plus cubes are always a plus. I would probably build it up as a 434.
turbo choice will depends greatly on horsepower goals, though with that many cubic inches you will have no problem spooling up a T-88 or say GT42 very quickly - which both will give you the potential for 1000+ rwhp - and both will keep the backpressure down allowing the turbo system/motor exhaust side to last much longer.
I definitely would stick with a efi setup, probably a Gen7+ DFI at this point - would be no problem making that work with your setup,and it would compliment the turbo much better than the stock LT1 pcm. (though there are things you can (should) do to make tha twork better).
Finally since you are going with a normal SBC you have a much wider head choice - go ahead and go with a decent set of 15 or 18 degree heads - you will make the same power at a much lower boost level (probably a bit more power due to less losses) - which means less stress on the motor, compressor, and exhaust. Plust much better octane tolerance.
But really it all comes down to what type of horsepower you are trying to make.






