To the best of my knowledge, both of those combines used 318s,...just like the ones in Dodge cars and trucks with no apparent changes.  The firing order for a chrysler V8 is Clockwise 1-8-4-3-6-5-7-2.  I am not sure about the valve clearance.  Are you talking about valve to top of piston clearance?  Because if you are it is miles.  Those 318s were all low compression and had pretty generous combustion chambers.  And finally, 318s were produced from the &#039;60s all the way to the turn of the century.  They have made zillions of them, and if you need parts, I would just go to Napa or AutoZone because you will get it a lot cheaper than going to an ag shop and asking for engine parts for a 545 Oliver combine!  Anyway...hope this helps.