why did you o ring the block and run copper gaskets??there is no need to do this .and the leak could be from the gaskets being to hard not dead soft or the o rings are to hi this may make it leak did you use hylomar on the gaskets ?if so take the gaskets out heat them they will truns color and put them in water this will make them dead soft use hylomar on them use thin sewing thread a round water pass this will make o rings you can try this but if the o rings on the block are to hi it will leak as far this hp run the blower faster you should be looking at ex temps so you do not melt the pistons out .from the look s of this engine this thing should make a 750 hp+ but is the blower teflon lined?if not you will have to go over to drive it closer to 1to1 i have runed a blower for 5 years a548 big block 10 to1 with 10 boost and used 10-17 fel-pros head gaskets no o rings or copper gaskets