Several brake hardware kits are showing and using a different type of brake shoe retainer. I received a kit with these new type spring retainers but could not figure out how to install them so I used the old pin and spring type. Here is a photo of what was included in the kit. Th espring is put through teh backer plate and the end of the spring is larger to hold in the plate..

The rest of the spring looks too fat to go through the backing plate too

Correct. The larger end of the spring will not go through the backer plate, which anchors it. I think these will work but I cannot figure out how to pull the hook end of the spring spring through the brake shoe to put the anchor tab on. I thought there might be a special tool. I didn't use these but though it would be interesting to know how to install them. The seller told me these are the 'new' version of retainers but, thankfully the old style pin-and-cap retainer are still available.

Id bet even the smaller diameter shank won't pass thru the hole for the pin either

The smaller OD of the spring fits very nicely through the hole in the backer plate. The larger end will hold very nicely. The problem is not fitting; it is the stretching the spring out enough to install it / get the retainer on the end.