Here's a table of Springfield Garand
serial numbers by year of manufacturer.
If you qualify to order a Garand from the CMP, you may be able to talk them into finding a Springfield in a serial number range that your grandfather may have carried in WWII or at least one of the years of the war.
As mentioned, these rifles were rebuilt several times over by arsenals or even unit armorers. All of the current CMP Garands are ones that had been loaned to foreign countries and returned to the US.
I got my SA Garand a few years ago and it turned to have a low 6-digit serial number dating to April 1941 so the receiver is pre-war. All of the other components are SA except for the barrel. It's a Danish VAR barrel and from what I had read, this company (VAR) made barrels for the Danish Army that were all equal to we would consider "match-grade".
But there are many suppliers that have surplus real USGI Garand components that are period-correct for a given serial number. Putting together a "correct" M1 can be very expensive, but buying a Garand that is a "shooter" and looks like a WWII-era rifle is not that expensive.
The thrill will be the look on his face when he sees a Garand again and even better, taking him to the range and handing him a couple en-bloc clips and a target
When I take my Garand to the local range, I always get people coming over to ask about it. There are a few range members that are WWII vets and they always want to talk about their experience. For those guys, I always have a supply of loaded clips ready to go just for them. I willingly hand over my Garand to them for shooting a clip or two. Some grin, some laugh, some cry.