I played one of these for 23 years (1970-1993) but in 4 string. Its called a kings neck. Very slim and fast.
 
Chuck.

I have a couple of Haggys. The first one I got was a HB-1 (the one with the swimming pool tin foil on the front). Tiny neck, looks practically flimsy but those pickups are remarkably huge sounding. I understand why these basses left such a mark on so many young players.
 
The second was a fluke score off ebay. I'm sure people didn't know what it was plus it had a repaired headstock break. It's a Coronado IV with the original Bi-Sonic pickups. It's all mahogany with medium scale neck that has a very comfortable profile. Not exactly a lightweight though. Four rocker switches - one on/off for each pickup and two preset tones for each. A sliding volume control with a protective towel rack to prevent accidental adjustments complete the controls. I wish it had tone knobs, but I won't monkey with it - only 810 of these were made.
In spite of that, 3 years ago what comes up on ebay but a gutted body and neck in perfect condition in the same finish! I had to have it and outbid a music store in Germany. Now it is 100% and I have to say it's a lot of fun to play.
 
I had a Swede bass for a while. They are short scale. It was truly beautifully made and weighed a ton. Unfortunately I just couldn't get it to sound to my satisfaction.
 

Got an alan wrench in there...succeeded in accomplishing not much of anything...I still don't know about this neck. At least the top strings aren't fretting out now. I like it, though...if I could get the action down it'd no doubt be really cool. Right now it's got that good sound of a 12 string acoustic guitar with the strings half an inch above the fingerboard...very Led Zeppelin 3.

I haven't adjusted the action on my Hagstrom 8 for years but I just took a look and I am at 4mm on the E fundamental string and slightly under 4mm on the G side. My guess is I could get it a little lower but I don't play it often enough for it to be worth the effort.  
 
Keith

The Allen wrench would need to be a metric size - they just don't match up with imperial, and you run the risk of damaging the hexagonal shape beyond the point where the proper wrench would still take.

Oh, I was definitely moving it. It just didn't seem like it was having any effect. I'll try again later, then maybe take it somewhere. I'm enjoying playing it. It does still seem like there's a weird twist to the neck up around the first three frets.

I wouldn't expect any twist like you describe. While a twist is possible the Hagstrom 8 uses an H shaped truss rod which generally provides for a very stable neck.
 
Are you trying to add more or less relief?  
 
If you tighten the truss rod (i.e. clockwise rotation) do you feel any resistance or is it loose?  
 
Have you tried adjusting it with less tension on the neck (loose strings)?
 
Here is a link to the neck and truss rod details.
 
One other thing that comes to mind is you say the problem is around the first three frets. Could it be the way the strings sit in the nut and you need a new nut with more height?  
 
Keith

There is one for sale here in PDX if anyone is interested. http://portland.craigslist.org/mlt/msg/2497564429.html
 
Nick

Keith,  
 
Thanks so much. Cool web page. I think I'll take some photos of the neck again and maybe that will help. The alan wrench I was using was troublesome and a pain -- it's part of a set that doesn't really fit in the short space between the neck and first pickup, so I'm not really making precise movements, but when I did manage to get it in there, there was definitely resistance.  
 
The nut seems ok. The twist I'm describing is a subtle effect...like the next slowly, almost imperceptibly, starting to corkscrew...it's so slight, it may be nothing, but it does become visible to me near the top of the neck.

Ok, here we go. What you should see here is the action up high and the action near the nut, plus the bridge again. Does the bridge assembly need to be lowered?  

 

 

I'm no expert but it almost looks like the truss rod needs a good tweak, maybe even the bridge. I just reworked an old Krammer 8 string recently, had a heck of a time getting the bridge set up right. even thought it had an aluminum neck I had to remove the last 2 frets and a small chunk of the fret board just so the strings could clear it when you play below the 7th fret.  
 
try lowering the bridge first, but from the looks of it the strings may bottom out at the top of the fret board, so you may have to play with both the bridge and truss rod to make play. if all ells fails you have a great wall hanger there

Based on the pics, I would think the bridge needs to be lowered substantially.

Believe it or not, in that pic I'd already lowered the bridge a bit -- the screws are getting pretty tight...but...here we go...

Ok, I got it. I just didn't understand how the bridge worked. The action came down great. Oh, yeah -- it's functional.