Tony,
Per Chevy Power Catalog, 6th Edition, BBC Deminsions are 23.63" from rear face of case to front face of case, plus 2.15" from front of case to centerline of damper. 3.47" from front of case to centerline of first pulley on crankshaft damper. Crankshaft centerline to centerline of stock exhaust manifolds 11.48". Stock exhaust manifold centerline in this drawing was almost perfectly lined up with the valve cover and exhaust port outside edge. Hope this helps. Sterling