I need to upgrade my Brakes 75 850

I have an AP Racing Caliper on the front and stock rear. Rotors are original.

The front feels inadequate.

I suspect the front master cylinder is stock. There is a 13 mm sleeve kit available on Ebay for around $70. Has anyone used this on their bike?

I changed the rear pads because I got brake fluid on them. I put fresh pads on the back designed for the factory disc. It still feels wooden. I'm wondering if I might need to rebuild the rear master cylinder. I don't believe the rear brake could lock up the tire. It's almost useless.

I read that using a 13 mm sleeve in the rear master cylinder doesn't improve braking much and is not worth the effort.

I LOVE THIS BIKE. But the brakes must be improved. It's just not safe.

I can machine brackets for new calipers. What is the recommendation?

Here is the link to the Ebay 13 mm sleeve kit. https://www.ebay.com/itm/135749778070

Andover Norton 13mm master cylinder with stock lines / calipers & Ferodo brake pads on my mk3 and I am able to make the front tyre chirp with a decent squeeze on the lever.

I swapped my stock master cylinder for a sleeved one back when Old Britts were in business. I also drilled my rotor and had it Blanchard ground by Trudisc . Stops just fine now .