ASA and PSIA Instructor
Join Date: Apr 2000
Thanked 55 Times in 53 Posts
Rep Power: 21
Definitely use the alu backing plates, maybe 3/8" or so and 1/2 to 1 inch wider all sides than the base of the cleat.
It is negligent that the cleats lack backing plates.
Installing such will be only as hard as accessing the undersize of the cleats.
Follow the instructions in for potting the boltholes and bedding the cleats from here:
No advice as to increasing size or not, all being equal bigger is better than too small.
Certified...in several regards...