I suggest you refer to carbine club newsletter #353, which is a report on the second Inland Block 2912520-3212519. It looks like Saginaw made the receivers from 3152520-3212519. Indications are that the majority of stocks reported were high wood oval. It does say a few low wood stocks were reported near the end of the block, but no indication of what # that is.
Report indicates that slides E379 & L379 dominated this range, with only a few reports of E169 or E279 reported , which may be reporting errors. Unclear data. three different types of L379 slides were indicated with and without increased dwell machining. No indication in the NL where the cutover was.

Reisch indicates Type 5 slides did not start until Sn 3,200,000, but he is known to have mistakes.
Welcome to the forum. I am by no means any expert, just reporting what I have seen and read.