Jake,
I remember building a while ago.........pay particular attention while assembling the crankshaft - go slowly and make sure all the bits are cleaned up properly and lined up when you glue them, or the crank won't want to revolve smoothly.
Also, I'd replace the little tiny tube of oil with some rubber grease - you know, that white stuff that plumbers use on the o-rings on the spindles of your bathroom faucets. It lubricates better and stays where you put it - unlike the oil which eventually heads towards the closest gravity source (namely, the centre of the earth) and makes a mess of the inside of the model.
The model I made all those years ago had a battery operated electric motor, and the spark plugs were wired with little bulbs and would "spark" when the distributor rotated.
Basically, just take your time, make sure everything fits properly (adjust the fit if you need to) and make sure the crank, cam, and rockers are assembled carefully, and the thing should work just fine. Test fit, adjust fit, test fit, adjust fit, etc etc etc - get the message?
Oh, another thing - make sure the mating (gluing) surfaces are clean and tight fitting, and use a good quality liquid glue, not the tube stuff. Clamping the bits while they dry is best. Again, patience!! Allow everything to dry completely before moving to the next step.
If you make the model look as good as the engine on the 1960 pick up, then you'll have a real winner to display.
Cheers
LeeTree