The winch line may be scaled as a vector, tangent to the drum, representing the line tension.
The point of contact of the tangent will be one corner of a triangle.
The rear bolt and the forward lower edge of the base will be the other two corners of a triangle.
I would solve the triangle assuming that the whole force acts on the back bolts.
That is the worst case and allows for deflection of the wooden base and or looseness of the forward bolts.
Both conditions may allow more strain on the rear bolts than may be shown by a rigorous solution of the division of forces between the front and rear bolts.
Do you want a rigorously correct answer, or a safe to build answer?


--------------------
Ohm's law
Not just a good idea;
It's the LAW!

The force on the bolts depends on what the piece of wood is attached to. As shown in your drawing, there are no additional forces because the wood will follow the winch wherever it takes it.

TTFN (ta ta for now)
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ok, you need to read up on free body diagrams. These include all relevant forces ... You show the applied load only.

The fasteners react this load ... in shear (Fx) and tension/compression (Fy).
The shear should be obvious, the tension/compression is the reaction to the offset moment.
Yes, the bolts don't normally carry compression, but it is a easy typical analysis for a working engineer.
If you want "truth" then the offset moment is reacted by a couple, fasteners carry tension and the compression is carried by the fitting base, typically a triangular distribution is assumed, peaking at the opposite side of the fitting (away from the tension loads)

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