Along with loop considerations, the 3050 may not have software disk ownership enabled, but the 3140 requires software disk ownership. If you type "disk show -v" on the 3050 and there is no output, then you have hardware ownership and will have to boot to maintenance mode (ctrl-c for special boot menu, then option 5) then at the maintenance prompt on each node type "disk upgrade_ownership". Make sure to follow the ugprade advisor and match the flash card code on the 3140 or netboot to make it match (3050 uses "e" elf code and 3140 uses "q" code). I usually upgrade the 3050 elf code to match the flash on the 3140 prior to the swap (using the e code)...then the 3140 boots just fine off flash then push the q code again so it replaces the e code on disk...and follow the instructions for disk reassign and destroy mailbox local/partner... then /etc/rc and hosts for any interface changes with the head swap.
Having both root aggregates on the same loop isn't my preference in case of a shelf failure..and ontap should give an informational message about this configuration....but you said you have 1 fc loop and 2 sata loops... with mpha, I would spread my root aggregate across both sata loops. You can move the drives with the system halted, then it will boot no problem with the drives moved. Assuming a 3 drive root aggregate with 2 loops, put 1 of the root drives on one loop then the other 2 on the other loop and then if a loop fails, you stil have your root aggregate available.
for example: with the two loops...move the 3 root disks so you have root across both loops and with disk assignment it doesn't matter if a mix in the loop/shelf to each 3140 node.
loop2 node1-aggr0-rg0-disk1
loop3 node1-aggr0-rg0-disks2-3
loop2 node2-aggr0-rg0-disks1-2
loop3 node2-aggr0-rg0-disks3