AS you can see from the above, an L section belt is shallower from to to bottom than a std A or B section belt would be and are used on sliding sheave ( varidrive ) pulleys
And conversely a V section belt is deeper from top to bottom than a std A or B section belt would be and are used by Murray as a deck belt.
If you have bought a std A or B belt then they will cause you grief and not last as long as a 4L or 5L would.
The pivot point on the tension arm flogs out oval over time and you can replace it or weld the hole & reshape it round but generally some flop there does not cause grief.
So your top belt is rubbing and burning on the outside ( 5/8" ) side where the writing is .
If that is the case then the sliding part of vari drive pulley is stuck or the whole pulley is running too close to the side of the mower.
They use the side frame as a belt retainer which is why you have to remove the whole pulley to change the belt .
Try putting it up on 4 jack stands so you can get under there with the engine running ( deck removed ) and watch what is going on.
If you pull both of the seat switch wires off you can then work the motion pedal while watching the double pulley.
AS you push the pedal down you should see the lower belt running deeper in the double pulley and the top belt running further out.
This should be a very smooth motion.
As the top belt runs further out on the double pulley you should see the idler pulley pull back and stretch the spring.
Try doing this with the engine running slow so you can see what is happening.
You can remove the battery, tie the seat to the steering wheel ( or remove it ) start the mower using jumpers and have our friend watching the belt from above.
Exactly how did you replace the belts, which pulleys did you remove / loosen to do it.