Just go with the K&N. It really is a lifetime product and you can rest assured it does a great job provided you service it by the book.

Also there's an air-box version (cylinder) for the bullet that's maybe not as high flow as the cone but there's lesser headaches attached to it. If nothing else you can confidently use it in the rains and extremely dusty situations, remember a k&n is a lifetime investment. This is the version I run. It's just more peace of mind, and doesn't compromise performance in any noticeable way.

These high flow filters have a very revvy predisposition and its easy to forget they can cause excessive heat when pushed, the cone version is always going to be higher maintainance, and really what's the point if you have to swap it out, come the monsoons.

If you do go with the airbox version get the direct tube from airbox to carb like on the newer classics. The old intermediate boxes have a penchant for air leaks.

My mech says if I need to fit in BS32, have to grind the head i believe...any suggestions

You'll have to decide if that's worth the trouble Try the 29 maybe with some creative jetting? Its bound to be better than the VM, that's for sure. I'm not sure what the manifold size is on the 535, but whatever you put there make sure it sits flush or the charge will get very turbulent on its way in, and you don't want that

i think suitable mods can be made to the rubber baffle for this. but check the opening of the inlet port on the head to compare.

There's no rubber baffle between carb and head, or is there?

there is a rubber baffle