Is the floor concrete in your shop, cuz scaffolding is cheap and easy to rent. Cheaper than building a manlift platform for one time use.
I have often thought of building a tall platform like you describe. I think it would be safe enough. Make sure you chain it to the loader somehow so it cant slip off the end of the forks. Make sure the forks fit inside tube so it can't slide off the forks. Make sure you are harnessed in, and you wouldn't want to be shagging the drivers wife either. That could really lead to some trouble.