Ken, here are some pics of the stock skid when it was still in my sled along with tunnel pics when I was doing the RX-1 conversion. You can kind of see the addtional gusseting & brackets that are on the ST's frames.
The last pic here actually shows the tunnel with the new skid, but you can make out how the tunnel is extended to a certain degree.
If you would like, when I get back home this weekend, I could do some specific close up shots of the tunnel as I did not remove any of the oem brackets & gussets. Hope this helps you a bit.
Rob