Lug Bolts and Studs and Nuts (don't go there!!)
The overlander and others of the same era have lug bolts with a 1/2'x20 RH thread. Fairly common at most auto stores.
To mount alloy wheels on an older coach I believe the best way is to replace the bolts with studs of the proper thread. These are to be installed from the outside of the brake drum. Make sure the stud does not extend into the braking surface as that is where the magnets make contact with the drum. This is not too hard to do as wheel studs come in many lengths. Studs should be a couple of dollars each for wheel quality studs.
For the lug nut you might consider McGuard lug nut kits designed for alloy wheels. These cost around $50 for a set of 24 which would serve well the 2 axle trailer owner. The nut is steel, conical, chrome plated and designed for alloy only. A near perfect solution.
Old trucks and old trailers . . . a comfortable combination!
A-6E All Weather Attack Driver, BUFF
USN Aircraft Maintenance Officer, Ret.
'91 Suburban R-2500 w/BBC
'78 Honda GL-1000
'72 Triumph T-100R Daytona