Another ALAN frame problem that is often discussed is that the bonding between lugs and tubes releases and causes the frame to be spongy. The tubes are also threaded into the lugs so they won't 'fall out'. Personally, I've never come across an ALAN frame that has suffered this problem. I do love the ride of the ALAN frame and they are not like the harsh riding aluminium frames of the 90's the ALAN's were more compliant. The ALAN's had a very glorious history in the sport of cyclocross winning many world championships so they must have had a pretty good structural integrity. Some may suggest that the riders of such events changed frames regularly but I wonder why a world class cycling team would want to put-up with frames that were unreliable even if they were being sponsored by the frame builder. 20+ years of wins at the elite level still impresses me.
I think you have a very nice mid to late '70's gem and it should build-up to be a desirable bike.
Here's mine and I love it . it's slightly different to yours as mine is an '83 frame I've owned it for well over 20 years and I still enjoy riding it. I did commute on it daily in years past and it never let me down - I'm 6' 1" and 95kg.
There are plenty of ALAN owners here and they all own great bikes.
Please excuse the red wheels - I just couldn't help myself one day when I had little to do.