I was issued a SA M-14 in February 1966 at Parris Island, and it had the non-ventred fiberglass handguard. At that point, all the wooden ones were supposed to have been replaced with fiberglass, and the initial vented ones were also surveyed and replaced. The vented ones were failing when rifles were used in training and combat to give Marines a boost/leg up over walls and obstacles. A properly issued and maintained M-14 was supposed to use the non-vented fiberglass handguard as of when I was inducted.
One other issue with wood, related to the Garand. When the upper handguard got hot, it got longer, subjecting the barrel to heat-induced flex, changing the POI, deflecting it downward. The fix was to trim 1/16" off the rear edge of the handguard. It may sound sloppy, but the handguard was supposed to have some front/rear play.
So whatever handguard you end up with, if the POI deflects downward when the rifle gets hot, be aware of the potential for this problem.
Greg