It might be a little late,
@Bakerda408, but here's what I did to minitub my 68 Coronet.
1) I cut the inside of the wheel well at the highest spot and trimmed the trunk floor pan about three inches (up to the frame):
2) I had to cut the trunk hinge support off the wheel well since the wheel well would be moved inward about 3". (My supports were rusted so I ended up fabricating new pieces -- see below.)
3) My wheel wells were pretty rusted in spots so I took the opportunity to replace pieces. I also added an additional 1/2" strip of steel to the bottom lip for strength:
You can see that I was gaining almost three inches:
4) I welded the inside to the frame which ground out pretty nicely:
5) Then I welded in pieces to fit the almost three inches of new wheel well. I had tried to create a single strip but didn't have much luck. I figured a good grind, some undercoating, and a little bondo on top and no one would notice my Frankenstein job):
6) I mentioned above that you need to relocate your trunk hinge supports. Mine were rusted so I fabricated new bottoms:
7) Grinding, some bondo, and a coat of epoxy primer and I'm happy with the results:
8) One thing I did not anticipate was that my rear seat bottom needed to be reshaped to accommodate the additional three inches of wheel well that now intruded into the seat. I simply bent some of the frame and wires to make it fit.
It was a fun project, especially since you can mess up and no one will ever see your mistakes
