Pulled the Bosch Plugs, no number on them

[Bishop]

Hey Guys,
My 89 420 started missing yesterday and I pulled out one of the spark plugs and it only says BOSCH PLATINUM, no printed number.
The dealer has always tuned the 420 before I retired, but now I have the time and I want to do it. I have always checked the plugs number when I have serviced my other cars in the past, but this is the first time for me to do the 420, and I see no BOSCH number. I figured the dealer has certain plugs he used, but these don't help me.

I'm going to the parts store tomorrow, and I wanted this boards input on which spark plugs to buy and everyones opinion.

It's a 1989 S420 with 155K miles and always runs Chevron 93 octane
gas, (As the dealer had reccomended).

Thanks