Mustache man, it's a huge leap of faith to simply fire up an engine somebody else "rebuilt".
If it were mine, I would invest a day and a gasket set and check all the bearing clearances with plastigage, put assembly lube on all the lower end bearings and on the camshaft, lifters and timing set, check the ring end gaps and correct positioning of the ring gaps on the pistons, verify correct camshaft indexing and set the lifter preload.
This is really not a complete list of things to do like verifying correct rocker arm-valve stem contact pattern to confirm correct pushrod length and degreeing the camshaft.
Use of a "true roller" timing set, if it doesn't already have one, will give you long term accurate valve timing that will show up when you check the ignition timing periodically and find that it hasn't become retarded due to a junk timing set wearing out quickly. A true roller timing set costs about $75, which seems like a very small price to pay for not having to replace a worn out junk $20 timing set with the engine in the car.
Reassembling it yourself will allow you to verify correct torque on all the fastners.
Don't forget to use a camshaft break in additive, get the engine ready to fire immediately before the break in lube is wiped off the camshaft and lifters by excessive cranking and run the engine at RPMs of about 2000 for the first 20 minutes or so.
Or, you can just fire it up and see what smokes.
