timing marks are very small and hard to see. On the inside of the cylinder head casting there is a small mark like a sliver divot. on the cam shafts there are small sliver divots on them. You need to align the divots on the inside of the head with the ones on the shafts, intake and exhaust at the same time.
my experience is that there will be pressure on the valve springs so you will need to hold the shafts in place some how. I fit a small jamb against the sprockets. I connect the chain on the intake side as there seems to be more room there. remember to take up all the slack on the exhaust side of the chain, as well as all the slack on the top roller between the cams shafts. once this is done you can put in the link.
Generally I try to adjust the am chain tensioner before peening over the cam chain joining link. its worth checking the timing marks once the cam chain link is in place and the tensioner is applied. Saves using up another single use joining link.
if you like i can scan the pages of the manual. I have the original CL450 Shop manual from a dealer. shoot me a message with your e mail and i can scan them some time this week end if you like.