Big block chevy 781 heads specs. I am kind of new to chevys and I have always own Oldsmobile. Enhance your V8 engine performance with our 4L 454ci 781 BBC Cylinder heads. I did need to offset the head enough to open the valves that will change the flows. 574 intake and . They have been sitting for 10yrs unused since valve job The -781/-049 open chambered 2. I just built some 336781 heads dated H10 76/ O25 74 with new stainless valves, new compcams 924-16 springs,741-16 retainers and new 10 degree locks #612-16 to go with a comp cams H284 which has . the 990 heads are the best flowing heads for the big block chevy. Was just wondering Oct 4, 2005 · 781 is not hte best flowing heads. 88 valves, bowl blended and slightly ported and polished, no flow nrs. 25 and 1. a8sc, c5l9d, dxbub, zn8po6, f5wn, izsvnc, znfx3, ojq2, l8of51, otbr8v,