I wouldn't think twice about it. Pretty common for people doing new wildcats before dies are widely available and 257 and 264 are about as close as it gets for something like this.
I've only experience with making 6.5 saum with redding 7 saum FL bushing dies before 6.5 dies were a thing. Worked fine.
Anecdotal and sample of 1, but Redding are the only dies I've ever had issues with getting consistent sizing and sticking multiple cases. I think some of that was because it was 280AI, but I've read others had similar issues with them being sticky with other cartridges.
I'm using the Hornady match grade die with an RCBS bushing for my 25CM and have only ran 100pcs through, but it was flawless operation.