From "Lee-Enfield No. 4 and No. 5 Rifles", by Charles Stratton:
Rear handguard, Second variation: "four long. grasping grooves, about 7 1/4" long...".
Both first and second var. rear handguards have been observed on No. 4 Mk 1 and Mark 1* of Brit., Can. and US manufacture.
The grooved handguards are "found most often on Savage-manu. rifles".
Both grooved and non-grooved are found on rifles produced in the same factories during the same time period.
"Evidently, the two (S and L) factories traded wood fairly frequently.."