Here is some info when I converted my brakes:
They are not listed for 58-60 Thunderbirds since they were not available. If you check under 1961 Thunderbird you will find them. The part numbers are Wagner H2512, H2513 and Raybestos H2544 and H2545. Napa also has them under their own part number. Most auto stores will have them or can get them. You can also get them from Rock Auto. They run between $6 and $10 dollars each. You need two of each side. You also need four of the self adjuster springs; Wagner H412. They come in pairs. They don't come in the kit.
Napa Auto Parts:
Frt and Rr Right side UP80696 $8.69
Frt and Rr Left side UP80695 $8.69