JSMvintage Do more than a flush, while the head is off dig the 60 years of gunk out of your block. Screwdriver and a hammer thru any coolant holes especially to the rear of the block. Had one once with intakes bent from timing gear failure,just a beater wouldn't start like it should,so just ground the valves till they cleaned-up. Went ahead and put it all back start run ride and drive for a long time then. In your case get new valves if bent,as I said mine was just a beater !!
