Sounds like an SS ,,they were the only Commandos w/ high fender.
A "S" was basically a Roadster,,,but with Upswept pipes,both on Left side.
And no front stay on the front fender,only on the rear of front fender
A "SS" was an "S",,,but had the High Fender with No stays,,
and Upswept pipes One on Each Side.
The Hi Fender and Pipes make it very distinct
'Sposed to be made 1970 and 1971 only.
But with what all was happening w/ Norton at that time,,
"anything is possible.
I do not know what tank capacity was,,,,usually they're reffered to as "small"
I always assumed that mean 2.25gal
This is the "correct" SS Tank and sidecovers.
Notice no "sculpting" or contouring on tank
http://www.precisionmotorcyclepainting.com/images/t-1970_norton_750_ss.jpg
They're Scarce,,,I've never seen one in real life
I hesitate to say this,,not want to cast aspersions.
Nortons in the USA have always been the more scarce
of the 3 most popular Brits,,,Triumph,BSA,Norton
Triumphs and BSAs seem to get "Customized".
Especially Back in their day,,,even when fairly New.
At least the pipes,,often the Paint,,,handlebars ,,various chrome bits and on down the list to full custom choppers,bobbers,fake-track bikes,,,or Real track bikes put back on the street
The Restoration craze is only fairly recent,,less than 20 years.
Nortons got their fair share of "customizing",
But what seemed quite popular was to convert 1 model to another.
The bikes per given year/model era were always very near the Same .
Seats,Tanks,Pipes ,and a few detail bits could make "any Norton" into any Model ya wanted.
Me Personally,,thought the High Fender looked terrible.
I can't imagine anyone Doing that,,,EXCEPT if they wanted to "Clone" an SS Model.
In that case it would be a Must.
What I'm trying to say is,,,,If You're looking to BUY,,,make certain that a bike presented as "original" is Actually The Model it's supposed to be.
And not a "conversion".
"A Rose by any other name.....",,,,,ANY Norton is a Treat.
Whether converted to another model or not.
Biggest difference would be in PRICE and future price appreciation of a conversion vs an original.
All that is just my impression of Norton Situation,,,and only from my limited perspective.
Which is not really worth the proverbial "2 cents" or grain-of -salt.
But I am certain,,,the High Fender is Definitely an "SS",,,and if it's got one Upswept/ High-Mounted exhaust pipe on each side,,,that just about clinches.
S & SS both also had "skid plates" on the frame,,,none of the road bikes did.
Some SS's had SS written on the side covers,,,some did not.
They all had 750 Commando lettering
.....................................
.............750
Commando
................................
OR,
..............................
..............750
Commando
......SS
....................................................................
There's a BUNCH of Norton Clubs and info sources,,
some remarkably knowledgeable places/folks in USA,Australia,,,worldwide really.
But the BRITS have always known Nortons better than Norton itself.
Any of such places can tell you Lots more about them I can.
Hope any of that helps
...........................
Edit:
Here's a site w/ the only pics of an SS I can find,it's got all the different Commandos w/ a bit of info on each.
Scroll down to see the SS
http://www.nortonownersclub.org/models/commando/commando.html