I started my 340 up this spring and noticed a **** load of blow by. I finally got around to doing some tests on it today. Compression is all over the map. There is light blue smoke coming out of the tail pipes. And you can see the amount of blow by in the video. The plug check showed all cylinders a little rich except #6 which showed a little oil fouling. The car still pulls like a freight train. Keep in mind this is 340 with a roots 6-71 blower on top. I am pretty sure a complete refresh is in order. Rings, bearings and a hone job for sure.
Since this engine was together for so long with zero issues is there anyway you fired it up this year on old pump gas. I just wondering if it got stale on you. As far as retorquing head bolts as often as you do you are stretching your bolts year after year if you aren’t replacing them. Good luck. Ohhhh I would put a machinist straightedge on those areas you pushed the head gaskets at a bare minimum.