it is not the intake for lack of the upper two bolts on each side i used many intakes that is not it .it just could be like said it may need more mile s on it .was the block plate honed ? some have gone to i very fine finsh on there bore then go over that with a plateau hone could be the rings are not hooking up good ?? hard to say .pistons could be abit loose but when warm they can grow abit so they would stop rocking a round in the bore helping the rings to seal .some of the old timmers do not like to run the pistons as close of runing clearances. with the new alloys they do not grow like a older TRW so they need about 1/2 of what we used on the trw less he could of set your bbc for kill and by that she loose . if there getting beat on hard with power adders as it would not be set up like for stock use .i would look at a better oil ? you did not say what your using .but i would only run a w40 or w30 in it for 500 or more miles before you go to a full synthetic and i would not wast money on it . it could smoke some tuneup could be off . you do not have a choke ?your oil could be getting fuel dump in it .as well as no pvc or poor breathers could be pushing oil out as well or abit of every thing .and big block s can use abit of oil with big bores and big strokes your beating oil up on the walls making a bigger job for the rings as well as the beathers or pcv your cr can add to this as well .a set of low tension oil rings can add to this