Grind away part of deck stringer to install backing plate?

[memelet]

I'm installing standup blocks for my running backs. The place where I need to mount them is partially right over a deck stringer.

Pics showing deck location and where the backing plate would be: https://picasaweb.google.com/memelet...PTOjvz3xbTPxwE

I suppose I have three options:

1) Grind away the stringer so the backing plate has a flat surface
2) Build up next to the stringer to make a flat area.
3) Don't use the backing I have and instead use individual washers (or two backing plates)

If I do 2, then I would have cut out holes in the coach-roof for the bolts and nuts to protrude. (My coach-roof is wood.)

If I do 3, then clearly I will not the full strength. 3 also has same the downside as 2 for at least one bolt.

So I'm curious about grinding out part of the stringer. Does the stringer need to be continuous to perform its function? Would a cutout cause a deflection point with excess stress? Would the backing plate make up for any loss of strength?

The boat is a 1985 Passport 42. (Brion T, you looked over my boat during the Oakland show.)

thanks!

-barry