I just gotta take issue with that. Perhaps crane or a book may say as a general rule, but most of the Datsun books also said you could not swap cam towers from head to head, which is again, false. I have done that many times, with no ill affects.
I have spoken and confirmed with Nissan Motorsports many years ago the cam data, and there is no difference in the cams for the hydro head and solid. See the thread from above for the cam info.
If you are worried about it, send me your hydro cam and the rocker arms, and I will run it in my solid head, or better yet, I will sell you my solid cam for 20 bucks plus your hydro one.
This is a datsun specific issue, and the hydro cam will work without issue in a solid head. For that matter, you could use a cam from an NA engine if you like, personally I thought they didn't work as well, but you could use it too, if you like.
In fact, I used a hydro cam in my 240Z turbo engine, as it came with a hydro head, and swapped it out for a solid head, and ran the hydro cam foolishly thinking that hydraulic cams are slightly larger then their solid counterparts to make the same rated power. Hence the call to Nismo.
Seriously, I will sell you my Solid cam if you are so worried about it 20 bucks, plus shipping and your M cam. There is not a difference.