Why do you want to change processors?
What is the make/model of your current motherboard and ram.
You can likely simply replace your 7400 with a i7-7700k and get more threads and a faster single thread performance.
If you want to use a 2700X, the performance will be comparable to a 7700k, depending on what you are doing.
To change, you will need a new motherboard for certain, and possibly new ram. Ryzen is picky on the ram it supports.
A new motherboard will require you to take some steps to preserve your digital license so you do not need to buy a new os.
It is possible that your current setup will boot. If so, you only need to install the new motherboard drivers.
If the old C drive does not boot, you will need to do a clean install of windows as well as your apps.
Worth is something only YOU can determine.
That said, I would not try to use the 2700X you have and would sell it.
When you ever have to change motherboards, try for the latest gen products