I opened the barrel channel on a M70 B&C Medalist for a Shilen #5 during a conversion to 416 Ruger. I did not use a forward recoil lug on the barrel, but do recall thinking that had I, it wouldn't have been a problem inletting it.
That said, bare in mind that I had the option of placing the barrel recoil lug where I wanted, had I used one. In your case you're bound to the location of the lug on the Safari Express 375 barrel.
I wouldn't be afraid to roughly locate where the lug would lie, and then poke around with a Dremel and see if it could be inletted. If you run into a little of the aluminum skeleton, I wouldn't be too concerned. The forward portion of the skeleton does nothing to to counter the affects of recoil. There are plenty of stock out there that only have the aluminum block in the action area.
