Eric: Please get the Chassis Service Manual, Operators Manual, and Parts Manual for your 1650.
Those manuals are a must!! (And I would suggest you get them BEFORE you attempt the ISO mount replacement...or any other service work for that matter!)
The operators manual shows you the correct way to operate the tractor, and the service manual shows you how to service and adjust the tractor, tolerances, procedures, etc. The parts manual shows 'exploded views' of parts assemblies, as well as individual parts, and the part number for each and every part/piece/bolt etc. used on/in the machine. The parts manual also helps to 'fill in the blanks' when you are working on your tractor.
Here is a picture of the old lower ISO mounts that I removed from my 1250....they are worn out/junk!
And this is a closer picture of one of them
Sorry, I don't have a picture of a new ISO mount to show you the difference.
It is possible to work on a Cub Cadet without a manual, however, for a 'newbie' it can be challenging. Also with the manuals you can use proper procedures and do proper adjustments...no more 'guessing and BSing'
Like Brian said, replace the snubbers, and I would also seriously suggest doing the Rail Mod as outlined/described by Richard C. You can also find the rail mod in the FAQ's.