The only way to know what you have is to yank a needle out and read the stamped letters on the shank. KD, DX, would be good.
One of the little myths circulating for years about SU's is the idea that changing the jet height will have influence on the total fuel curve. It won't. Jet height controls mixture strength at idle. Above idle the profile of the needle determines the fuel curve. That means you'll have to change needles if you have a lean pair in the carbs now. Even float chamber fuel level has a limited effect on fuel curve in these carbs, whereas on fixed venturi carbs like domestic cars used to use the change is substantial.
If you are using full power, as in your plans to race the engine, then 7's will be needed. And achieving a good rich mixture will be even more important.