Technical Water leak

Have a brand new french block build flat head has Dyno time and a little road time very little every thing was fine just started it up and drove it in my garage didn't even get up to temp everything was good came out the next day water all over the garage floor was coming out the header have open headers haven't investigated any further yet to frustrated to even think about it had to pull engine once before because of a piston problem engine only been back in for 2 weeks. Had Dynoed it and retoqured heads a couple times everthing thing was good and than this . Any way was reading some of the threads on here and will look into those but my question on the French Blocks is the exhaust bolt holes I used studs with thread sealer on them they on these blocks go into the water jackets can anyone on here verafie this for me and could this be the sorce of my water leak maybe need a better thread sealer and also mabe some bars stop leak for some insurance . OPEN for any ideas or constructive comment's Please
Thank you Guys
Clyde