Rebuilt 340 been sitting for about 5 years

When we would get reman'd engined from Jasper they would have plastic plugs in the spark plug holes. We would turn the engine with a breaker bar. The plastic plugs would POP when they came out proving compression. So in it goes and fire it up. Tiny sparks that came out the exhaust manifolds as the rings would seat may have been rust particles. No clue how long the engine had been sitting before we got it. Same applies to any reman'd engine out there. Oil in the cylinders could interfear with proper ring seating. Bite your lip and let'er rip.