Tom,
It looks pretty small to get it accurate using such methods... though there's always trying again! How many of these things do you need? Two, four? It sounds like you started with the slots then tried to get the rounded ends, maybe it's better to drill holes at each end of each slot first, then cut beteween them. That way you're using something consistent, the drill bit, to achieve the holes which will then act as the guide for the cutting. If you need more than one identical piece you could clamp them together while the holes are drilled, so at least they'll all be in the same place on each piece.
Alternatively, have you thought about making your own photo etched parts? If you have good access to a laser printer (black and white will do) and a shop that sells hobby electronics materials, it's in fact not that hard. You don't need tanks and aeration systems, just some zip lock bags, an incandescent lamp to provide some heat, and a paint roller. Advantage is that if you can draw the piece you want on a computer (using Word will do probably) then you can reproduce it several times exactly and you can achieve something quite intricate. I assume you're not trying to achieve that angle on the slots? Just the slots!?
The only issue you might have is that you want the holes to go right through the piece, which is harder to achieve as you need to be able to transfer your design to either side of the metal sheet - but that is possible.
Let me know if you want any more info on that and I'll give a bit more time to the reply.
Matthew
The last attempt had me cut the grate holes as the appropriate size rectangles and then add in the bars, fill and sand the ends and that's that. Sat back and did not like the results. the bars are hard to get set correctly and evenly. And no one that I've found makes and aftermarket deck conversion to the earlier version of this vehicle.
