It is possible to put a 5.3-liter engine from 2005 into a 5.3-liter Chevrolet Silverado from 2008, however it is not recommended owing to the complexity of the process. The Silverado 5.3 from 2007-2014 utilizes a 58x crank and 4x cam, which are incompatible with the 2005 engine. Consequently, it is required to switch their positions and install a new front cover.
This is not suggested unless you are a qualified technician due to the labor-intensive nature of the operation. In most instances, it would be simpler and less expensive to simply replace the engine than to attempt to install a 2005 5.3 into a 2008 vehicle. This is what the confirmed Chevy Mechanic did in the preceding question, having just completed the process of removing the motor for exchange.