is there not a small aluminum tag on one of the float chamber screws, if you have that I can identify what it originally fitted?
However as the 1275 Midget had 2 x HS2's as standard you'll have to experiment a bit to find the right needle although I'm sure someone here has a similar set up.
It's on the large side for an otherwise standard 1275 engine - but it will work. Use a BDL needle. I believe the Spridget bonnet needs a 'hump' to clear the big single carb ?? Best check before you slam it shut........