Bit surprised the Cross Race came with Ultegra. My Cross Race Pro of a similar age has 105. Is it definitely that lever?

edit: I see Tredz say the cross race was 195 cable disc and cyclist.co.uk say the Pro that year was Ultegra. Guess yours is a Pro?

So I think the st-rs505 (105) should be fine but the hood shape might be slightly different, that could bother you. I’d be tempted to try the 180mm disc option. But the rotor itself is the best part of £70 I think.