I only have PEMS on my car and really need a downpipe to open up my exhaust up top...but I'm making ~300whp with the cam and 3.0" pulley. Most cars will lose low-end torque with a downpipe unless they're flowing pretty good...something to keep in mind...
3800performance.com sells the Hogan downpipe for the H-bodies.
As for the idler pulley...they're easy enough to replace. If it'* the tensioner pulley that came off...look into replacing it with a 3.5" metal pulley for more belt wrap if/when you start dropping */c pulley sizes. You may need a shorter belt if you're running a stock */c pulley...but it'* something to consider.
I really need to change my screenname since I'm hardly in Tampa anymore and no one can remember the current one correctly.
1996 SSEi: swapped INTENSE 4t65 trans, INTENSE GEN3 LSD, 3.69s, 3000 stall ATI converter, S1X cam, WBS stage 3 intercooler, full P&P gen3 M90, 2.8 MPS, N* TB and LQ4 maf, 4" FWI, TOGs, full 3" exhaust, and a DHP Powrtuner to keep it all in check