Not hard but I wouldn't try to copy CB designs.
Lots of them are all show and no performance.
If you want to try it, you just scale ALL the dimensions by the ratio of the frequencies... all the element diameters, lengths, and so forth.
If you want a good 2m or 70cm beam, you should build a better design.
for some easy ones.
I don't know if the Joe Gunn and Moonraker engineering is reasonable or not. The claims made for gain and front to back are just stupid.