As everyone else has said: Clean Clean Clean! & also Measure!

Other things to look for:
Crank end-float: try & make the rear side of the 2 thrust bearings parallel.
Oil pump: if you a reusing, replace the spring as it gets a good hiding since the pump is very oversize for the job.
Oil pump O-rings: I like to use a regular O-ring to back up the orignal style ring.
Assembly lube: make sure the cam & lifters has plenty of Moly grease or Lube from a cam grinder on it. For the rest of the engine, just use oil.
Priming: after you have buttoned up the sump, turn it right side up, pour in 2 litres of oil & crank over the oil pump with a big screwdriver down the hole where you would put the drive gear. After a short while it will come out the side, put the filter on & continue. After the filter is full it will come out the top of the block from the rocker feeding passage, you are now certain your oil pump is good to go.
Startup: After you have the motor in the car & the head & rockers are bolted on, turn the oil pump again until oil emerges from the rockers, now you can put in the drive gear & distrubutor & set the timing statically. Assuming you've taken care of the water & fuel side of things you are now ready to start. Assuming that you still have 2 litres of oil in it already, pour another 2 litres into the rocker cover just seconds before you crank it over for the 1st time to start it, hopefully you will have some still pouring over the cam when it fires up. Do not let it idle!, speed it up to 2000 rpm & keep it at 2000-2500 for the 1st 20-30 minutes of it's life. This is when the camshaft is breaking in. After this 30 minutes set the timing & shut it down. I would now drop the oil & filter, check the cam, adjust the tappets & refill with new oil & filter. For the 1st couple of hundred miles do not rev the enginge, do not lug the engine & do not baby the engine either! Try & keep it between 2000 & 4000 rpm & use plenty of full throttle between these speeds. When you are confident all is well, change water & put in some coolant. After 500 miles change the oil & filter again & continue on as normal.