just replace one on my 235. some help would have been nice! man that is one heavy chunk of iron. i bought a couple of bolts that matched the head bolts and cut the heads off for guide pins. after warming motor fro 30 mins or so, very important to retorque head bolts. i referenced torque specs and patterns from
http://chevy.oldcarmanualproject.com/shop/1954truck/index.html
good luck. cc