Front frame rail/a arm advice needed.

Car was in a front driver's side accident long ago, and fixed not so well.
It looks like someone held a welder in a few places for 5 minutes and called it done.
They also put a patch on the front, and welded the k to the frame in one spot.

Putting on a suspension kit, and of course, the top a arm mounts are rusted off the rail, split, and with the crappy welds it is a mess.

I bought a piece of a rail years ago, but it does not extend to the floor.

I researched, and I see you can buy the frame rail caps, where you weld these over the existing frame, and you can buy the a arm mounts and weld those on.

I talked to a body guy, and he said he could weld the swap meet piece on, but he would have to also weld plates on to strengthen it, and would prefer a new rail and floor pan.

This is where I need advice.
If the current rail is a mess, and probably not perfectly straight, the new cap may not fit, and it does not address the a arm issue. A new complete rail does not exist.

Is the partial rail I have a good solution, or should I look for a used complete rail?
If the driver floor has rust, do you need to replace it in order to replace the entire rail?
Are the new a arm mounts a good solution?

Please help, my daughter is not happy when she cannot ride in the Barracuda!