8" vs 10" finbox

I currently shaping a 9' longboard and only have an 8" finbox.  I can order a 10" but was wondering if 8" will do?  Would I place it at the same positon (back of box) as a 10".





The length of the box obviously depends on the fin you want to use.  With a 7" box, your options will be limited.  Placement would be the same as a 10" box towards the tail, but if it’s 2+1 the box need to be placed relative to the side fins.   Typically, 7" boxes are only used in 2+1 configurations and only on thin HP longboards.