It is good that you plan on feeding blocks as that ensures they will receive the nutrition they need
My suggestion is to forget about making a mix and instead give them blocks in a dish, and a couple of times a day to give them vegs. And occasionally give treats.
The recommended diet for rats is
1. a good quality block (Oxbow or Harlan Teklad 2014 are recommended), free fed makes up most of the diet
2. a variety of daily vegs such as baby kale, broccoli, organic carrots, mixed greens, cauliflower, peas, organic corn (GMO corn is designed to kill rats), cooked sweet potato, baked squash, etc
3. healthy treats such as a piece of fruit, berries, cooked grains (such as oatmeal, quinoa, buckwheat, etc), organic pumpkin seeds etc
Rats need low protein, and it is best if it comes from plants
Whole foods are much healthier then processed food, especially highly processed foods
Avoid foods containing added sugar, salt or fat
btw water that is free of chlorine and fluoride is essential
http://www.ratshackforum.com/forum/showthread.php?t=15227
There is a forbidden foods list
http://www.ratshackforum.com/forum/showthread.php?t=590
Here are some links to useful info
http://www.ratshackforum.com/forum/showthread.php?t=22782
http://www.ratshackforum.com/forum/showthread.php?t=3708
http://www.ratshackforum.com/forum/showthread.php?t=2046
If you want to learn more about nutrition, this is a good site: nutritionfacts.org
hope this helps