I'm putting this into my MG Midget:
A15 bored .02, crank turned .01/.01, balanced.
H89 head pocket ported and port matched to GX manifold.
GX intake with a pair of HIF4 SU carbs from an MGB. MG heat shield sectioned to fit.
A15 electronic dizz.
Either modified 1600 header or factory exhaust manifold (I've seen pix of it fitting, will check).

Spoke with Delta Cams and detailed the build and the intended use and was recommended the KC grind (262D, .425 lift at valve) regrind of my A15 cam. $56USD. Said I could use my stock valve springs, maybe shim them if I have float.

So I am pretty sure I will have some lean spots with the stock needles in the SUs.
According to SU data the AUD550 carbs have ABD needles & AUC4387 piston springs.
Funny thing, keen-eyed as I am, I noticed that the SU is not a Holley or an AFB so I'm kinda lost.
Any thoughts if the stock carbs will be OK or if I should get some tune-up parts (and where does one get spare needles and springs for SUs?)?

We use the Hitachi su type carbs - needles are available from Nissan. I would ask an MG forum about S.U. tuning parts.

There are two main tuning parts:
* dome springs
* needles

Springs don't seem to be too critical, Datsun only used two different ones on everything from 1.2 liter to 2.0 liter. Apparently they will affect sprightliness but not flat spots.

Needles affect everything. Start with the stock M83 needle and see how it works for the modded A15.

Another factor is the damper oil. Its not official tuning procedure, but some guys fit lighter or heavier oil to affect throttle transitions. Nissan recommended 20W or 10W30.