I built a couple different short blocks using that Canton louvered tray. Both were 4.250 stroke cranks, one hit and one didn't. It wasn't much and I made it clear, but it had to do with the rod bolts themselves. They were also two different manufacturers H-beam rods. The Callies Compstar with L19 bolts cleared, the Eagle "3D" with L19 bolts did not. Interestingly enough the Eagle's bolts had a larger head on it. It only hit on two rods. I just pried the tray up until I had about .060 clearance and ran it. There was no indication of any witness marks upon teardown.
I think the louvered tray that had clearance issues was the Moroso early on, not sure though as I have never used them. The Canton screen trays cleared when I have used those with 4.250 cranks and SCAT rods.