A few rear suspension questions

67 dart. I want to move the leaf springs closer to the frame rail, move the axle back a 1/2" and install sliders in place of shackles. I am fabricating the front leaf spring mounting brackets out of 1/4" steel using the out-of-stock DrDiff offset kit for inspiration. For moving the axle back I plan on moving the leaf spring bolt hole in the front mounting bracket back 1/2".

For the rear I want to use sliders and make essentially this 1730481165800.png but have the slider on a slight angle since someone mentioned in the thread where I pulled this image from that angling it would be beneficial.

Car was a slant6/904 convertible that will get a 400b/833. The rear will be explorer 8.8. I want to run about 27" diameter tires in the back. I am using new leaf springs that I bought at Carlisle over 20 years ago that I thought were "Super Stock" but have no idea at this point. Maybe someone can tell something from this:

1730482106721.png

My questions are:
For the front mounting bracket, is there an advantage to moving the leaf spring bolt hole up or down any amount compared to the stock position?

What angle, if any should I use for the sliders?