your talking about clam shelling your forearms,but you shouldn't have to. I have big hands and I got them to fit,its a tight squeeze on and off but they fit.I used a 16mm cover strips for a bit of extra room though you can make the strips a little bigger if you want.
just remember to remove all of the return edge at the wrist,this helps a lot.
For the shins I used the original closure method hooks and elastic or you can use Velcro.
The cover strip here is 25mm.You can see the holes for the hooks use here.For the Velcro method, just run a strip of heavy duty Velcro down the length of the shin armor,male side facing out away from your body