Here is just one of several ways to help solve your problem.
You didn't state the size of the machine screws, and with that in mind, it may be cheaper and easier than what I am suggesting here to purchase
the fasteners as has been suggested at boltdepot. You might also try Fastenal.
Keeping in mind that a winch base invokes far more of a sheer force compared to tensile, you don't need to have really long bolts, but the block has to be well secured to the deck. That being said, you can screw/glue the block in layers and at a thickness below the winch you feel comfortable with (1 1/2" should be sufficient) install STAINLESS tee nuts to match the windlass
bolt pattern. Then you can use shorter machine screws to secure the winch.
A simpler way would be to fasten the support block with threaded rod, then use shorter heavy fasteners to secure the winch. People with fiberglass
boats and aluminum
masts seem to forget how winches were/are attached to sitka spruce masts, it being a light soft wood.
I have a wooden boat with wooden masts and use either heavy wood screws or flat/oval head
sheet-metal screws. A number 14 screw is approximately 1/4".
Incidentally, Fastenal has oval head
sheet metal screws on clearance (if still in stock) that are cheaper than plain steel
. I was able to purchase
a good variety at an incredibly low price
. There is often, but not always enough clearance above the base of a winch to use oval head screws.
Another way would be to imbed a drilled and tapped plate in the "tower that supports you winch.
Is it about time, skill or money
? That is a choice you will have to make.
All the best