Need help with engine mounts/perches

[Ghost's68]

I’m down to just figuring out what mound to run so I can finally drop my LS3 in. I bought some DD sliders and have them on the block now but the POL perches I bought don’t sit flush on the rail of the truck. Reading the instructions I see it says it might need modification to make them work. I don’t want to bend my rails if I don’t need too. I was thinking of getting the CPP and even buying the 73+ style.

What’s the best approach here considering I’ll be running LT headers?....