If I understand correctly, your 10 year old son is going to be playing on 2 different teams at the same time?
You probably will get a number of views on this site.
Here is one:
He will be pitching for both and playing 3B for both and their games will be at different times and days during the same week?
I assume he has different coaches?
It isn't the distance that should be your main focus, it is the number of times he throws that distance and how hard he does it and how much rest he gets.
Assume he pitches a game for the travel team and then 2-3 days later they want him to pitch for the rec ball??
Assume he pitches for the rec ball and the next day/2days later they want him at 3B for travel and to pitch in relief.
Just my view, but the focus needs to change.
10 year olds are very susceptible to growth plate injury/damage, amongst other issues.
The issue isn't primarily dimensions, it is how many pitches on each dimension as a pitcher followed too closely by 3B and more pitching, and and how they are all thrown, ie., velocity and breaking balls or both.
Growth plate injuries are painful and can have lasting issues if not appreciated.
Take this one from experience...mine, and ours never played travel, just little league. Take ownership of your son's health and arm health now. Read and make sure you know about growth plates and injury and mitigating/preventing to protect your son.
Plan in advance how you will deal with him pitching for 2 teams and playing 3B and avoiding over use and getting him enough rest in between. You and he won't regret this later if you do.
If he is 12/13 and having overuse issues, whatever he does as a talented 10 year is not worth it!!!
Good luck.