After further investigation on another forum I found that a Scorpion yt12cl fits right in and costs $63 to your door. The MagnaPower ETX15 Dekka costs $77 and is a tight fit. This information from folks who have done it. That batterymart UT12cl does indeed cost $57.96 but with shipping comes to about $71.
1971 R50/5, 2013 G650GS
DRZ400S, KTM 250 XC-We
XR200, 1947 James ML
'Falling off motorcycles since 1963'