1988-1994 (and of course older pre-gmt400 trucks) the wiper switch is separate from the multifunction switch. It's operated by the multifunction lever, but electrically, the only switches that are literally part of the multifunction lever are the cruise controls. The wiper switch is separate and lives inside the column housing. It is indeed a different part for intermittent vs. non-intermittent. It will come with its own wiring pigtail.
Apparently, there are 4 different wiper switches - w/ and w/o intermittent, w/and w/o tilt wheel. So be sure you snag the right parts.
Obviously, you'll need to change the wiper motor, too.
You may want to look at the factory service manual for breakdown of the steering column before tearing into it. It's a little bit of work. Links for the factory manuals online can be found here on the forum.
(and just an informational tidbit - basically all electrical functions in the steering column are separate switches on the pre-1995 trucks, instead of integrated into one mf switch like 1995-up. high beams are operated physically by the mf lever, but it's a separate switch down on the column. wipers are a separate switch. turn signal/hazard switch is separate.)
Richard