I'm running spacers on all four wheels, but mine also adapt from a 4X130mm bolt pattern to a 5X130mm so I can run Fuchs wheels from a 911. They're about 1-1/4" thick and I've been running them for 6-7 years now with no issues. Mine are from Pelican, were custom and pretty expensive, but they're very high quality.
I bought a 3-foot length of metric, threaded bar stock (the same as my lug bolts) from McMaster-Carr and cut mine to length, then screwed them into the hubs/drums with Locktite Red to hold them. There are a bunch of places on the Web (Pelican again comes to mind) that sell different length and size studs that would work so you could continue to use lug nuts.
You'll be much safer with ring spacers of the appropriate thickness than what's on there now.