The longest ride I've taken on my '83 was 400 miles in a weekend. A good seat, comfortable bars, and a 23/48 sprocket combo helps. The 23 hurts acceleration a little, but REALLY lowers the rpm's at highway speeds.

 

With my old -74 ironhead I rode 580 miles on weekend, no problems... just check everything before you go.
I was riding about 50-70 mph and mandatory pit stops for refueling after 100-120 miles.
I didn't even take any tools with me ( I don't count letterman supertool )

 

I rode my 72 RIGID from OKC to Daytona last year, a little over 1300 miles each way with no big issues, I have a Crane HI-4 so no points issues, I lost my tag somewhere in TX, but thats it..... well besides no feeling in my butt after about 5 hours, made it down there in 2 1/2 days, back in 2.... left on Thursday morning got there Sat about 3 in the afternoon, left the following friday night and got back sunday night, I also rode it to Vegas 3 years ago on its maiden voyage so to speak after I got it 1150 miles, I left OKC at 6 am on Friday and only stopping for gas, I was in Vegas at 10 PM Friday night....... I decided then that I would not ride that far in that short time ANYMORE... it wore my A$$ out. Get yoou Ironhead and ride the hell out of it, you'll never regret it

 

What do you think people did in 1975, ride a Honda?

 

I was going 70 to 90 Kmiles between topend rebuilds on my '76 and the bottomend was good for about 5 topends. And, that was an XLCH with no oil filter!

As for long rides, I rode it to pretty much every major run on the west coast and to the Yuma Prison run, usually with a passenger with little or no trouble.

 

I've done quite a few 300 mile a day trips on my 79. I'm usually pretty sore afterward and my legs feel like jello. If you want to do some long freeway trips consider changing out the drive sprocket and rear sprocket to get you better rpms at high speeds.

 

If the bike is in good shape you should be able to ride it as long as your but will let you.
I rode a '62 Triumph 650 as my only transportation for 2 yrs and during the summer I would ride it 500-600 miles on the weekends, everyone told me "you can't ride a triumph on the freeway" it held up just fine. The motor co. sold the sportster (XLH)with a touring package in the 60's and early 70's. so the factory figured that it was ok to tour on.