If only someone supplied a slimline rotary table.....
That would not have solved your problem.
I too have major clearance issues for some setups, and I have a much deeper throat on my mill.
Everyone is striving to fit a chuck on their RT, including myself, when in fact an RT is a lot more versatile than that.
The slimline one you were looking at was just too limited in the accuracy stakes, you may as well have used a lazy Susan with felt tip markings around the edge, and later, when you learn how to use the vernier hand wheel and dividing head, you will be thanking everyone for

you down the road of the one you have bought.
Oh! ye of little faith.I have most probably only achieved a height saving of about 10mm by making my new backplate, but every little helps.
My biggest problem solver has been to use dedicated spindle collets instead of a collet chuck. They have saved me about 50 to 75mm in the fight against clearance issues. To such an extent, I very rarely use my ER collet chuck any more.
Also, people say, why do I need so many drill chucks? By using the smallest chuck for the drill that I am to to be using, I can save myself precious mm's when it comes to a tight for height setup.
I don't buy tooling just for the sake of it, there has to be a reason for it. The difference between the smallest and largest chuck is about 35 to 40mm in gained clearance. Maybe the difference between getting the job done or not.
So it isn't just your RT you have to look at, you have to scan the overall picture to achieve what you want.
Bogs