never seen these gm manifolds before , and what motor is this ?

[MAC67]

hey guys , i was strolling through my local scrap yard today and stumbled across a wierd chevy small block , its not so much the motor that wierd , its the exhaust manifolds , the block number is a 3892657 which shows up as strictly 67 camaro , but that number was put on 302's , 327's and 350's , for the 67 camaros , if it was the 302 would it be worth very much ? the balancer looks to be a regular size balancer but it has quite a few holes drilled in it , factory ones , not home done , ,, now to the wierd manifolds , they have gm stamped into them , the dump out in the center like a ramhorn but they are straight across , now the really wierd part , they have a collectopr dumping straight down like a regular exhaust manifold , but they also have a collector coming straight out of the top , so there is 2 places to hook exhaust to on both sides, up and down , have any of you guys stumbled across these before ? or any ideas on the motor ?