Well i am doing this on my 190 2.3 now. I am sure there are more bolts off than when i swapped out engines. On mine i have had to pull all components off front to remove timing cover, then lift engine high enough to remove oil pan. Then fight with those damn slide pins, broke one, and cant get the one out which the tensioner pivots on. I think i will need to drill out that one. For me this is a pretty big job!! The time in hours seems about right. But i dont know for sure with yours being a 2.6.
You could just replace chain, upper guide rail, and tensioner(not tensioner rail) in much less than 25 hours i am sure.
1988 190e 2.3 with 91 engine