Hi, I have had the exact requirement like this.
I needed to have M strategy for fixed bin, to limit the quantities being picked from fixed bin.
Then we needed to check the reserve but only for entire pallet quantity on TO.
First settings applied to 001 - fixed bin or in your case your storage type 003, are M strategy with limiting quantity.
Second, picking by user exit (ZXLTOU07), in which we have written ABAP code to check the transfer order required quantity against materials full pallet quantity.
If these are equal, or required qty is bigger than pallet qty, pick, if not, skip.
I won't be able to share the code at the moment unfortunately but having the
solution implemented successfully you have a model on which you can base
your customizing / coding.
If you need more clarifications I will be happy to help you.
Regards.