When replacing the cracked mast, I made very precise measurements and placed everything on the new mast section. Most rivets were 3/16'", but there were eight 1/4" rivets on the goose-neck and two 1/4" rivets on each spreader. Each spreader also had two 1/4" bolts. I basically copied 100% the way the cracked mast was built, on the new mast, rivet for rived, bolt for bolt. The new mast works great, no issues in raising or lowering.
On the Low tide issue: I got up at 3:15AM just to measure the water level at LOW TIDE. I had 2' 4". What a relief! I still plan to dredge out a 12 inch deep area under the centerboard, just to be safe.
I appreciate all the comments, advice, and suggestions. I'm new to sailing, so everything is new to me. (30 years of powerboat experience).
-Adrian