Hard Drive Sleds for PE2950

I have a PowerEdge 2950 with the SAS6/iR controller (part CR679) and the 3.5x6 SAS backplane (part PN610). This server came with two 500GB WD Tornado drives mounted on the D962C carrier with the PN939 Interposer. I want to fill the remaining four slots with 1TB drives but cannot get any clear info from the site as to which carrier I need and if I need an interposer card. I am hoping to get enterprise-grade SATA drives (probably WD) on the open market.

Any insight or suggestions on the sleds/interposers I need or how I can figure out what I need?

TIA.

-Larry