Access to timing marks

On a 12.7 Detroit can you access the timing marks on ALL front gears with the front cover on. through the access covers

 

Thanks for responding !st the put new cam on new head and the clamed that the timing was off. then they removed the front cover they didn't explain why. I was under the impression that you could access the timing marks on the gear with the cover on .when I asked what he found when he removed the cover he couldn't or wouldnt give me a definitude answer something stinks

 

I have no idea what there doing ,when they removed the front cover they said everything was fine !!!!!! 23 hours to remove the cover to tell everything OK

 

what manual are you talking about and can you send me a link i have the 60 ser manuals