The only issue I see with that is having to mix only as much thermal transfer epoxy as one can apply in a under 4 minutes, as it takes a minute of mixing it.
My Meanwell has 3 larger heatsinks on the sides of the casing, but I only did one at a time, mixing a small separate batch for each.
Also since epoxy is exothermic, after mixing it, if you keep it in a thick pile it will get hot enough to start smoking, one needs to spread it thin after mixing thoroughly. The bigger the batch the more possible exothermic reaction and possible wasted epoxy.
And I do not recall the Arctic Silver thermal epoxy being cheap.
But the heatsinks are great. The extremely loud 40mm internal fan of my Meanwell only comes on after 15 minutes at maximum output(40 amps), and turns off at 34 amps in 85F. A 10 amp improvement over no additional heatsinks. At 75F ambient the fan never comes on at all. When new and before I added fans to the case lid, the fan would cycle on and off at 6 amps output.
I should have added them when Westend first sent me a batch, but procrastination is the first step to any process, and I tend to get stuck on that first step.
Since I have a bit of overkill in my middle name, I was considering adding small heatsinks to the threaded 'bars' which pull the transistors tightly to the casing via a screw or 3 through the middle.