Stock dp can be used, but I do recommend a 3" smooth bend downpipe if you plan on running the boost up there, and or maxing the turbo out. There have recently been some good posts about downpipes. My personal opinion is, a replacement downpipe is warranted once you get into the low 12's and want to go faster.
The factory heat shield bracket will need to be modified in order to get the heat shield re-installed tho. This is because the turbine housing bolts to the cartridge differently than an older T3/T4 series turbo. 4 bolts bolt the turbine housing to the chra vs 6. And the orientation of the dog eared bracket that connects to the heat shield question mark bracket is not the same. Unless PTE has recently addressed this issue within the past couple of months.
The GT3255E was specifically designed from the beginning to displace the TA-49 and TE-44 on cars with a stock D5 converter. It does spool up faster and will make slightly more power than a TE-44 at higher boost levels. This is due to the GT series compressor and turbine wheels used on the GT3255E.
You will also need a different wastegate actuator that is specific for the GT3255E if you are upgrading from a stock or TA series turbo. The bolt pattern on the actuators attachment bracket is different.
Hope this helps.
Patrick