Paul, the sheath for the 165 works better for the 153UH/160OT than the reverse. The blade envelope of the Golden spike is slightly smaller. So the 165 will fit, but is sometimes tight. The 153/160 will fit in the 165 sheath just fine. The difference will be in the handle strap if that is the style of sheath. The blade of the 153 is about 3/16" shorter, and the width is about 1/8" narrower. Excluding the handle circumference, there should be no problem. The guard is slightly smaller as well, so a pouch style may require a tighter fit?
THE 160OT has the same handle and guard as the 165OT, but a plain (flat) ground full tang blade patterned after the 153UH.
Arnold has several of these Golden Spikes, and I am sure he'd be willing to send you a loaner for pattern making. If not, I'll send you mine. Don't be shy about asking for patterns!
Michael