Converting the 26" hardtail to 'modern' gravel

[Fatal Swan]

Many thanks for the responses! Actually my plans for this bike have just been shelved. After a fair amount of trying to fit square pegs into round holes with this frame I've ended up going down the actual gravel bike route - or more accurately I suppose, a CX bike set up for winter road use. Something suitable on ebay came along just before I'd committed to this build...