step 18
http://chevy.oldcarmanualproject.com/shop/1948_51truck/51ctsm0613.htm

torque specs
http://chevy.oldcarmanualproject.com/shop/1948_51truck/51ctsm0648.htm

per above
15-20 ft/lbs for center manifold clamp bolts
25-30 ft/lbs for end manifold clamp bolts

I torqued my heat riser bolts to 30 ft/lbs