I have yet to upgrade mine as well. Went with a Wilwood Classic Series manual 4 piston setup on my '68 Cougar, but I would really like to do factory parts on this one, so I hope we BOTH get answers. Mine is a '65.

The wilwood kit DOES work pretty well though, and you don't have to change spindles.

The 74 - 75' Granada brakes were being used to replace mid sized fords ie mustangs and torinos..  I really would like to keep my Galaxie drum spindles.  some of the aftermarket kits adapt to this heavy spindle. They have a hub built into the disc but many have a weak looking caliper mounting bracket.  

I just completed a four wheel disc conversion on my 61. I wanted to avoid after market stuff as much as possible simply because of budget. Wildwood stuff is nice, but comes with a heavy price tag. I went with discs all around because of the visibility thru the rims and lastly I was going restomod.

I considered Granada fronts originally because using those will also lower your front end. I backed away simply because I was a little concerned I would have no control over the amount of lowering I would end up with. I discovered you will see between two to two and a half inches of lowering with a Granada spindle and brake swap. There is a supplier on line that supplies complete kits and are priced fairly reasonably.

I ended up going with a 78 Cougar spindle and disc swap. They were sourced from a local salvage yard and were fairly inexpensive. Parts are readily available and cheap. They look good thru the rims. However, this swap does create a camber issue. The best camber achieved is 1 degree of positive camber. That is at the top of factory spec by the way, but too much for my liking. If this is an issue for you, then avoid this swap. Your other option is to keep your spindles and go with an aftermarket disc brake kit that uses a caliper bracket to work with your factory spindle. I didn't go that route because I didn't like the calliper that was included with the kit I had sourced. I like the clean factory look of the Cougar caliper.

As far as rear discs, again, budget was the deciding factory. I went with 84 Lincoln discs and an aftermarket adapter kit. The kit was around $150.00 and works well. Brakes were sourced at a local wrecking yard.

I went with an Astrovan M/C and hydroboost system. The M/C does the job but it could be better. I don't really care for the long brake peddle travel required to engage the brakes. That M/C is for a disc/drum system and the bore size is a little too small, so not correct. I have a larger bore M/C for disc/disc, but am hesitant to install, only because the fluid reservoir is fairly large and unsightly. I am using an adjustable proportioning valve.

As mentioned before, my budget was a big factor in deciding which way to go once I decided to go disc all around. My total investment was around $550.00 all said and done. As with many of the modifications I did, I discovered that when you change something, sometimes you end up with a result you didn't see coming. Those unexpected things can always be corrected, it just takes a little more time and work😀