I had a repair shop for 20 years and I found that the GM warranty process was easier than the process for other engine builders. It is spelled out that any modifications or changes to a new engine will void the warranty, and it makes sense. The documentation for all of the add on parts(invoices) and documentation of the mileage at install are key points. I have had instances where a vehicle would come back with a engine that had failed. Of coarse the people just say it died, must be a bad engine. I always put little heat tabs on the frost plugs on the side of the engine and rear of the engine. If the engine was ever over 240 the center would melt out of the tab. While a warranty claim is difficult with proper documentation it can be taken care of. The issue of having it installed by a dealership or certified mechanic can be a non issue as long as you have all the documentation for the add on parts used, dates, mileage and also records for maintenance after the installation(date and mileage for oil and filter changes ect). I'm sure some have horror stories of not getting any warranty because of different reasons but in my experience if something really failed because of an issue with the motor I always got reimbursed. I know that Jerry (Hotrod Lincoln) does some field inspection work for warranty companies, maybe he can chime in with some words of wisdom.
