the arty is very heavy and while the griffins may be able to lift a cannon, aiming and firing it would be another matter. not to mention even if they did manage that, its quite likely that the ones carring it would have their limbs ripped off by the recoil of the cannon firing.
There is a reason that even in the real world and cannons were made extremly light for river barges, they still tied them to the side to stop them from being pushed off the otherside of the boat/ship
Here is my solution:
We create a rigid platform lifted by rope and harness.
On the underside of the platform is a turn wheel with a corrosponding wheel on top of the platform from which it can be turned.
Hanging from the underside wheel is a long rectangular platform that has a set of winches used to angle up and down by either end a second equally sized platform underneath where the actual cannon is housed at one end.
Both ends have barriers carefully sized to keep the cannon from sliding off, the other two sides have walls, and this bottom platform even has it's own roof.
The cannon upon firing slides back on wheels both on top and bottom secured inside of steel rails while a harness and a set of pulleys and geared winches act as brakes helping to dissipate recoil before the cannon can hit the back of the platform fast enough to damage anything.
The cannon platform is accessed by a set of side doors, containers tied down and secured on the sides of the platform act storage areas for ammunition, and rope mounted containers on the ceiling act as ballasts. Harnesss on the sides help griffins stay in place while the cannon is aimed.
To prevent a fire from breaking out due to Sparks from the rails the interior of the cannons housing is lined with clay coated cloth.
We can fire the cannon down at an angle from a platform without the ball falling out prematurely and going straight down by having the cannon be breach or rear hatch loaded, the barrel be ever so slightly wider towards the rear, and having the cannon balls have deformable protrusions that are bent back when the firing charge goes off.
Why would you want to be able to fire a ball down at an angle? To minimize the time needed to move a cannon into a good position to fire, to minimize required trajectory estimations or calculations, and to allow easy firing on anything that manages to approach from below.
This platform is capable of being lifted and operated by a team of griffins, however due to weight only when mounted on airships can this be used often or in substantial numbers.
By constructing the platforms primarily out of wooden beams, cloth, and rope the weight is kept relatively low. We will need to figure out which of the wood types available with sufficient strength have the best strength to weight ratio.
We will need to figure out which rope fibers perform best.
As for airships:
Considering the way clouds when magically enhanced can support solid weight, we should try seeing if we can enclose them inside of protective cloth envelopes and use them to support airships.
Does temperature effect how much weight clouds can support or for that matter their strength?
How does water density effect the strength and floating weight capacity of magic clouds?
How long can magic clouds go without magical maintenance?