Unsafe? Not so long as it fits properly. It will handle differently if the geometry different.

Basically, your head tube is the straight line you need to measure off of. Using the center line of the head tube, draw a line straight down towards the ground. Then draw a line from the center if the dropout, up through the centerline of the fork blade, to the head tube. From this you can measure the fork angle & the rake(measured from dropout to the centerline of the head tube, parallel to ground.
Also good to know is the offset of the wheel. From the head tube centerline to the ground, you measure to the center of where the tire hits the ground. On a 74 deg head tube, 2 to 2-1/4" makes a really nice handling bike.
Drawing this up On a piece of paper can be really helpful. When I built my frame, it took measurements from the bikes I had & transferred them all into autocad & tweaked them to fit me a little better. Cad is a lot easier to work with, once you get through the learning curve. It really allows you to easily make changes & find results