yes you can use the 273/318 ones (assuming the 273 is a hyd lifter cam). no opinion if new is needed. on mockup check the lifter preload to find out if you need different pushrods & go from there. I wouldn't think you would need custom lengths but if so watch the straub industries utube vid on "rocker arm geometry". No apologies needed, we are here to help & be helped! (I learn every day I am on here). the treasure trove of info that the guys here posess is off the charts. RR
