If you have the sunsport seating with the VDO cluster, it's likely the RS, the RX (which I have) has the standard seating with individual gauges. Both were available with I/O
Also, the beam should be 8'. 9'10" is quite wide for an 18' boat
The 5.7 is a very large motor for that ride. I can run about 47mph with the 4.3, however I am nowhere near 2000 ft elevation.
Here are the specs for the RS:
http://assets2.fourwinnsmarketing.com/past_product/specs//1998/04%20Horizon%20RS%20(p10-13).pdfYou can also find the owner's manuals at
http://www.fourwinns.com/past_product/owners_manuals
_________________
-Rob.

Current boat: 2011 Yamaha AR210
Previous boat: 1998 Horizon RX 4.3GL SX