If the engine was properly balanced it will last forever as long as it is not starved for
oil. If you were to run your engine 24 hours a day for 4 months you would have 144K miles at 50 mph. We will run compressors at 12,000 rpms for 8 to 9 years, 24 hours a day!!!!! If you engine builder was good enough to get those results he was good enough to balance and ensure the proper bearing clearance etc. My only suggestion, warm engine thourghyly prior to romping on it.
You may want a big block if you like to:
1) overheat
2) poor fuel economy
3) In some cases adjust the valves every 1K miles
4) modify
oil passages and hope they were done right
5) probably put up with
oil leaks
6) Fills up the engine compartment
If I was going big block it would be all aluminuim 482 stroker, in other words $$$$$$$