The only chipsets that were validated to operate with the Pentium Pro were the 440FX (Natoma) and the 440KX/450GX (Orion) chipsets.
Neither chipset supports SDRAM....only EDO and Burst-EDO RAM, up to 1GB of either type.
SDRAM was first introduced to the P6 Family with the 440LX chipset, due to the additional bandwidth requirements of the new AGP bus.
While SDRAM did exist at the time of the Pentium Pro, chip densities and the relative "newness" of SDRAM made it both impratical to implement large enough amounts, and guarantee stability in systems where generally the Pentium Pro went into servers.
Portland and Atlanta refer to the names of the Intel motherboards, PD440FX and AL440LX based on the FX and LX chipsets respectively. Other Intel FX boards include the VS440FX Venus, PR440FX Providence, AP440FX Apollo and the server class BB440FX BuckEye.
While there were some slotket adapters made for the PPro from PowerLeap, chances were that they wouldn't work on most LX boards due to lack of BIOS Support as well as the usual voltage problems. Unlike the Pentium II, the VID and VRM are a little bit different and not always included on the processor.