Do anyone know of a link to mounting 21in. split rims and tires?

Can't post links with the phone, but try picture googling with some words like split rim 21" mtfca and you'll find some in old forum threads.
I'm swapping tires and fixing flats today, you need some kind of tool to crimp the rim to get the tire off, and to expand the rim with tire, tube and flap in place.
There were special tools for that back in the day, but I haven't found any so I use a turnbuckle. A shorter turnbuckle that goes between the two ears closest to the split may be even better..

Picresize.com has gone sour I think, many pictures that looks good before resizing now looks like crap after..? Must try another free online service next time.

This may help.

You Tube video

https://www.youtube.com/watch?v=j0PFSgAt06w

Here is another good video
https://www.youtube.com/watch?v=DYh1PVgpbjo

Here 2 other videos from Coker Tire.

https://www.youtube.com/watch?v=LWwkVM5ddSo

https://www.youtube.com/watch?v=lRyJYoIc7vs

There is a three position rim spreader/shrinker tool. The tool allows you to pull the rim inward to overlap the rim for ease of removing the tire and also to spread back into place after the tire is installed. I see these tools at every swap meet, I couldn't resist and bought three of them. They fit in the lug holes to pull the rim inward and fit against the inside of the rim to push it outward.

A shorter turn buckle will work better. The rim spreader if not used properly can damage your rim, also I find them cumbersome to use and heavy to keep in the car. KGB