that good news,great feeling aint it.in a scrap yard after some van bits the guy was starting a huge lorry engine,same as ,just sat on its sump pan, I was amazed as it ran fine, he blipped it, didnt even rock half as much as yours, for its size I would guess 7 litres there abouts, just a tad noisy tho.
any engine I have worked on makes me smile when it fires up, even simple jobs like cam belt change, if all runs good , ye great feeling, admitedly more so when its a crank up rebuild, great satisfaction, even better when engine is still sweet 100k later ....
Yup a bit gut twisting...untill its done a few k,s. As long as the rebuild hasnt had snags though ,but that little gremlin might have done something eh......hence the bated breath untill initial smoke clears...ha.