Again, a couple Mk1 questions (and others)

[bronson@inwave.com (Nate Mellom)]

1:  How hard is replacing the heater core in my '81 gonna be?
2: Would it make any sense at all to install the extra idle stabalizing 
system I have on one of my spare engines?  ('84s got it, the '81 
doesn't)  I had a recent tune up done on the '81 (idle set, mixture, 
timing, etc), and now my idle seems a bit iffy.  It'll idle high 
(1500RsPM), then swing lower (1000RsPM)...I dunno of the later idle 
stabilizer would do me any good.
3:  I'm going to be swapping the clutch off of my (not so happy) engine 
out of my '84 with my (hopefully much happier) engine I got from Jasin 
(urGTI@aol.com).  What, exactly, is involved?  I have the clutch 
alignment tool, but once I get the flywheel off what happens?  Do I need 
to worry about aligning things and stuff?
4: Anybody got one of these? 
<http://abacus.sj.ipixmedia.com/abc/M28/_EBAY_64215416eb2fc314946db4f205/i-1.JPG> 
(VDO voltage gauge).  I have the matching oil pressure and temp gauge, 
and I'd be willing to trade a set of Audi gauges (oil press, temp, 
volts), all in perfect shape, for one.  I'd like a matched set, I really 
don't like the Audi gauges.

I think that's it for now.
G'night!!
Nate
'81
'84

Oh, and I have a bunch of engines, mostly complete, I need to try and 
get rid of one of these days.  All 8v.  Lemme know if anyone's 
interested.  I'll be willing to give you parts for shipping.