To clean up the rough surface left by the angle grinder, and to make the board flatter, I planed the both sides by hand.
The small block plane left the surface smooth enough that it barely needed sanding:
I jigsawed out the rough form of the deck, and cleaned up the edges with a plane and some coarse sandpaper.
I did not want the bolts that hold the trucks on to split the wood, so I added aluminum plates to the top of the deck, to spread the load from the screw's caps. To make the plates level with the surface of the deck, I routed depressions for them. The edges were finished by hand with some tiny chisels.
The plates were epoxied to the deck, and drilled for the bolts.
To prep the wood for finishing, I sanded the wood progressively to up to 1500 grit sandpaper, leaving the surface extremely smooth and almost polished.
Rather than applying some sort of varnish or polyurethane, I finished the sufrace of the wood with tung oil. Tung oil gives the wood a lovely color, waterproofs the surface, and (in my opinion) looks and feels nicer than a clear coat that adds material to the sufrace of the wood.
Here's a comparison of the oiled vs unfinished wood:
And here it is with the trucks bolted on. As usual, I used countersunk stainless steel socket cap screws.
Once I get some wheels, it will be ready to ride.