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Rip off the lower edges, graft on extension pieces, pin and glue, reshape to fit, dab of stain and blo and Roberto's your tio!

https://www.milsurps.com/images/imported/2021/05/20210503_1319039d6b4dec39a2ccbd-1.jpg
https://www.milsurps.com/images/imported/2021/05/20210503_1319260c1267c23255c53f-1.jpg...

I bought some repro grips on ebay a couple years back for $20 USD + S&H. Included fasteners. Ill-fitting but holding a place until I can find something better. I will post pictures later.