I don't think the technical details for the 1998 range were ever put online, but the 97 and 99 seem very similar, so the following which is from 99 probably applies to 98 also:
"Cross-Country Dual Suspension
MANOMANO, MOKOMOKO, KING KIKAPU
Kona Cross-Country dual suspension bikes are suited for lightweight, cross-country trail performance. Ideal for long-distance mountain biking & cross-country racing. Frame without shock weighs less than 5 pounds. Lightweight components are used throughout. The latest in Fox suspension shocks, Air Vanilla, with Air Negative function is featured for high efficiency and light weight. Not recommended for downhill racing, dual slalom, tricks or stunts. Not designed for double clamp suspension forks - warranty is voided.
- Active, rising rate design built around a Fox Air Vanilla shock.
- With a leverage ratio of 2.33:1, the rear wheel has 3.5" of travel.
- Main chainstay pivot is located 30mm above the horizontal hub axle plane, minimizing "pogo" effects caused by changes in the effective chainstay length. This location keeps the drivetrain length very consistent. It also helps to eliminate pedaling force from activating the suspension.
- Rectangular tapered rear stays connect to cold-forged swingarms
- Cartridge bearing pivots on seat tube/rocker pivot, bushing and bottom bracket yoke.
- Custom valved Fox Air Vanilla (Manomano), Fox Air Vanilla R (Mokomoko) and Fox Air Vanilla RC (King Kikapu), all with Air Negative spring function."
The striking thing is that, although you are under the impression that moving the seat tube/rocker pivot is part of the design, there is no mention of moving it in the technical notes. You're also saying that one of the settings is a DH setting, but the description makes it clear that the MokoMoko was designed as a light xc bike and not as a DH bike.
The advice that Paul is giving is also in the tech doc, but you have to do that anyway to get the sag correct and you adjust the sag by adjusting the shock, not by moving the pivot.
I may be wrong, but I don't believe there is any intention that you move that pivot at all - I think you should be using the position on the corner of the V. I agree with Paul though - don't believe me, write to Tech@konaworld.com
for authoritative advice.
There are modern bikes which you can reset to a DH mode, but this is generally in relation to setting an adjustable fork to max and by lowering the bottom bracket, so as to slacken the head angle right off, which is what you need for DH. But as you say, the 98 MokoMoko is a retro bike by any sensible definition, and I don't think it was designed for anything like that. It's just an XC bike.