I want to do a b18b1 with b16 pistons and a ls head what do I need to do in order to build it right and not have it blow on me? what baseman can I run ?

 

No basemap. Use zeal calculator with your measurements (most are pre-selectable), and calculate it out. Make sure you adjust for head milling & block decking.

 

do you know if I will need a b16 crank pulley ?

 

Your crank pulley from your LS is perfectly fine. Has nothing to do with the pistons you're using.

 

and what octane gas will I have to use ?

 

Always use the best fuel in your area from the pump, be it 91-93octane. Even compressions of 12.0:1 have been done on 93octane fuel without issue. But that depends upon your tuner's abilities in addition to your own mechanical inclination and machining. Go through that Zealautowoks calculator and plug in values to find out what your " 'round about" static compression you'll be.

If you're thinking you can run on "cheap" 87 octane fuel for any of this, please stop now, and just run the car stock.