In the past I've had some major issues with using aftermarket parts from suppliers that are not licensed by the engine manufacturer, primarily with the fit, finish and operating life. I've spent a lot of time verifying the size and fit of critical parts such as bearings, liners, pistons, rings and valves before installation. In some cases I've rejected up to 25% of the parts supplied or spent many man hours modifying the parts to bring them within the engine manufactures tolerance. Unfortunately depending on the vintage of the engine and the availability of OEM parts you may be stuck with aftermarket parts.
In today's market where even engine manufacturers are now outsourcing the fabrication of parts and recycling parts one should be careful of parts being supplied as OEM parts.
Troubleshooting 101 "Don't over think it - K.I.S.S. it"