4 1/2" or 4 3/4" bolt pattern?

The adapter doesn't look large enough to have an offset and from what I can see the shank looks centered with the upper flanged section.

Checking with an older tire shop can many times net you what you need.

Hitting the bigger swap meets you'll usually find a lugnut/adapter guy that carries all the different lugnuts and adapters you'll need.

How thick is the hub on your wheel?

What kind of rear axle are the wheels going on?

What's the lugnut hole ID in the wheel proper?
If it's something like 5/8" or so, you can insert a bushing that's a touch shorter than the wheel hub thickness, add a thick washer on top and use a regular nut to hold it all together.

The above assumes the wheels are the bolt pattern you require.