1. The precision of the of the 'slot' will be vitally important so that the shackle PIN in is FULL contact (half of the diameter of that pin in full contact) with the 'hole' ... and not winding up with a 'point to point' contact which will quickly begin to 'ductile' DEFORM fail until the ductility relieves itself to make that FULL contact. Shackle body vs. that slot (pin aft and shackle body forward) will be 'point to point' contact unless you precisely form the interior face diameter of the slot to match the profile shape of the shackle.
The shackle body to eye-splice connection will be better than point to point contact and will allow for some 'rotation' if the lines of stress are 'offset' from the boats centerline.

2. Id beef up the thickness of the plate at that 'terminal end' by a factor of 3 as 'saddle' joins are vulnerable to developing 'happy smiley face' fractures ... 'splits' emanating at 90° to the axis of the applied stress 'saddle'. The added
'thickness' would also increase the 'face to face' contact. The two added side plates to the main plate could simply be 'seal' welded to the main plate ... make that plate end as wide as the opening of shackle.

3. I'd beef up the underlying FRG structure to 'three times as strong'.

4. What is going to hold this all together to the boat and will increase the bearing capacity of the fiberglass ...... inner plate to match the outer plate and with the bolts PROPERLY TORQUED to at least 75% of the breaking strength of the bolt ... torque up 'several' times using 30 weight oil as the lubricant. The torque from the bolting will 'prestress' the FRG in *compression* and make the attachment to the boat MUCH stronger .... and the **developed friction between the plates and the fiberglass** is what transmits the stress, not the bolts in 'shear'.

'Nutherwords, I'd put that shackle PIN facing forward; keep the 'overhang' of the 'chainplate' as absolutely as short as possible AND precisely make that shackle pin fit *perfectly* with a full face contact vs. that 'half hole' ('a saddle'), and 'thicken up' the end of the plate thats hanging out .... and be damn sure to properly torque those lubricated bolts, shoulder bolts preferred. Build the whole system *3 TIMES stronger* (in psi near that slot) than the webbing or rope thats holding all those drogues together