I use the target of 50.... for myself. That higher level is mostly driven by the MS specialists. If you don't have MS, or worry about cancer (level of 70 recommended)...

Then you just need 2,000 IU D3 more than you are taking now.
The general rule is 1,000 IU for every 10 pts to raise.

A "normal" magnesium test result does not mean much. That test is only good for identifying very very low, or very very high levels which give dramatic symptoms in the ER. Chemo or diuretics can give very very low mag results. And people with kidney failure or who abuse laxatives may be very very high.

So you may improve with the Morton Epsom Lotion daily (a quarter's dollop size amount) or with oral chelated forms at 1/2 the RDA. (the RDA is 350mg a day), or by eating more magnesium rich food sources.
http://www.slowmag.com/

I use Puritan's Pride brand D3.