Mid ptos are slightly different than front and rear ptos. Generally mid ptos are designed for equipment built by the manufacturer of the machine. Like mid mount mowers, brooms, snow blowers, etc. They often times have weird splined output shafts.
Rear and *most* front ptos are generally universal. Meaning the splines on the output are standard practice.
With that being said, you noted that it looked rather light.
First off, 540 rpm converts HP to torque. You'll get more torque off a 540 then you will with a 2500 rpm. 2500 rpm will give higher horsepower, but less torque. But you get the same amount of power. However, the 2500 rpm shaft doesn't need to be bigger.
To throw some maths out here... The relationship for a shaft driving something is simple: power = speed x torque (with the right unit conversions, of course.) So by increasing the speed, you can deliver the same power using less torque. 540/1000 = 0.54, or only 54% of the torque required to deliver the same power at 1000 RPM, vs 540 RPM.
Hence why if you look at the drive shaft of a 2500 rpm MMM, you'll see it's this tiny, puny little thing, compared to a 540 rpm rear mount drive shaft.
1000 rpm ptos are commonly found on larger 75+ HP tractors (and some smaller tractors as an option). Most of these are for mower conditions, hay balers, etc where they benefit from this "perfect" reduction. It also saves fuel and wear and tear.
Now in terms of your situation, I don't know if there is a 2500 rpm to 1000 rpm converter. I know there are 540 to 1000 rpm converters, but they incredibly expensive. You might as well use that as a down payment on a machine that has a 540/1000 rpm gearbox built in from the factory.
When I was working on the farm when I was a kid, we had two or three implements that ran on 1000 rpm. I remember having to pull the snap ring out and swapping output shafts. I also remember the time I got distracted and FORGOT to put the snap ring in.... the noise it made was horrendous. Luckily I didn't break anything.
