Ok, so I just did a google search of both part numbers (98633126108 and 98633116301). Here are some websites describing each:
For 98633126108:
04 Porsche Boxster 986 Engine Splash Shield Bracket Plate 98633126108 | eBay
2000 00 PORSCHE BOXSTER 986 2.7- ENGINE SPLASH GUARD SHIELD BRACKET PLATE 98633126108 - WolfAutoParts.Com
https://www.delebil.no/artikelnummer/98633126108
The last one is the most interesting. I don't speak Norwegian, but I'm pretty sure it says that the original part number was 98633126108 and the replacement part number (if you want to buy it from Porsche) is 98633116301.
For 98633116301 (very few images):
Suspension Subframe Reinforcement Bracket for PORSCHE |98633116301
Rose Passion - P160136 - 98633116301 - BRACKET - Porsche BOXSTER 986 2003 Boxster S 3.2 CABRIO MANUAL GEARBOX, 6 SPEED > REAR AXLE ASSEMBLY > REAR ARM
Suspension Subframe Reinforcement Bracket for 2000 Porsche Boxster
I'm fairly sure that these are the same part, and Porsche just got sneaky and changed the part number on us to try to obfuscate enough to get me to buy a $300 replacement part. Or maybe I'm just reading into this too much...
Anyway, I'm happy to try the 98633126108 and report back with my findings!
Alex