If it helps any one with Omega Saloon, etc., there has been extensive well researched effort made by a poster on Cadillac Catera (equivalent to X30XE Omega Saloon) as follows,
https://www.cadillacforums.com/threads/suspension-conversion-kit-for-catera.121726/page-3#post-1836104I have excerpted some of the information to give you a flavour of the post,
BILSTEIN (Opel/Vauxhall)
-Strut - B4 Gas: part # VNE-4480 (OE Replacement)
-Shock Absorber - B4 Gas: part # BNE-2861 (OE Replacement)
-Strut - B6 SPORT: part # VE3-4425 (Firm)
-Shock Absorber - B6 SPORT: part # B46-2260 (Firm)
-Strut - B8 SPRINT: part # VE3-4426 (Firm/Lowered)
-Shock Absorber - B6 SPORT: part # B46-2258 (Firm/Lowered)
-Boot & Bumpstop: part # ASP-C245 (front)
KYB GR2:
-Strut: # 334903
-Strut Mount: part # SM5285
-Shock Mount: part # SM5287
-Strut Boot & Bumpstop: part # SB101
MONROE
-SENSATRAC Rear: part # 5786
ACDELCO
- 560227 Shock Absorber
- Alternate Monroe MA825
Cheers