I, too, was all worried about making this block "perfectly" to spec... and I did spend the extra time (with my mediocre-at-best woodworking skills) to make it pretty close to what the plans called for-- only to discover what you seem to have already realized: it doesn't need to be perfect.
Basically all you're trying to do is clamp the skin down tight so you can bend it up and around. You'll need a good assortment of clamps, wrenches, strength, and patience; but as long as your wooden block is solid and at least as long as the bend line, and has a straight >90-degree bend radius, you're pretty much good to go.
Good luck, and 'enjoy' Section 29 (insert Nelson "ha ha"

)!!!!
__________________
Mike Jimenez & Sarah Hammonds
EAA Chapter 33 Prez & Soc Chair
Marion, IA USA
RV-10 In progress! (N165MJ reserved)
-Emp & Wings complete
-Panel wired up, working on Fuse & Finish
-Blog horribly outdated (sorry)
-Too many distractions, we will finish the plane someday!!!
http://mikeandsarahrv10.blogspot.com/
http://www.eaa33.org/