Your title is the definitive indicator of what you bought - hope you got a title. If you don't have a title the 10th digit of the VIN will tell you the model year - V for 97, W for 98, etc. and the 6th and 7th digits will tell you the model - 70 for a 430 and 72 for a 420. You're not alone but it never ceases to amaze me how many people don't know what car they own.

PS - either way you have a 722.6 transmission and need the MB fluid.