When Bachmann started making On30 trains, along with the HO track, they used the standard for HO couplers, which is 25/64" above the rails. Most On30 modelers stick with the HO standard Kadee #148 coupler. HO couplers at 1:48 scale are a pretty close match. So, the use of HO couplers for On30 trains is plausible, as long as you aren't trying to replicate a specific prototype that used the larger couplers, like the D&RG.
Louis Pacific Northwest Logging in the East Coast Post count: 5000 posts added to below count.
Every one saying #5 OK, but the #148 Whisker Metal Coupler will work anywhere a NO.5 Coupler will work and is a direct replacement for most Bachmann On30 couplers & a direct replacement for most plastic Medium Centerset "clone" couplers.
Louis Pacific Northwest Logging in the East Coast Post count: 5000 posts added to below count.