You've got no chance of knowing what the km count was unless you get a hold of specific information of the car it came from !
The only way is to have seen the car the car the engine came from to check the odometer, or service book records...or if you personally knew someone with the car before...
If it was from a wreckers, I would never trust what they say in this regard !
You could always check with the RTA to find out what you can with the engine type and numbers and vehicle it came from - not sure if it'll reveal much info that way though...
Otherwise just get a good grease monkey to check it out for you and give it a compression test at least, if it's still in the car ?? you can get it pretty well looked at to diagnose its current condition regardless of travelled km's, but if it's already out of the car it's pretty much a case of owners onus...