Another big block tower question

[Radford46]

I’ve got a 68 c10. It came with the 250 inline 6. I’m converting it to a 396. I bought new, after market, bb towers a couple years ago when I started gathering parts. After some set backs in getting started, I started fitting them and they don’t fit. (And I cant remember where I got them!)
The bottom hole when lined up makes the top 2 ‘pop up’ about an inch from the frame holes and it seems like the frame needs to be trimmed about 1/4” from the inside edge to accommodate the brackets.
Well, I figured the aftermarket ones were off,Since everyone claims aftermarket stuff sucks, so I invested even more money in a pair of the originals. Same freakin fit!
Does the frame need to be trimmed some? I’ve never seen that mentioned, but I’m wondering.
A little help?