Carb intake boots

Hello, 
I was trying to remove the stock rubber carb intake boots since they are cracked, and I am having some trouble. At the time, I was unaware they are JIS, so they are partially stripped. Anyone have any suggestions on how to remove them?  
Thanks

You say partially stripped, what's stripped the "x" on the head or the threads?
If it's head then heat the thread intake mounts with a paint stripper hot air gun a few times to break the corrosion hold then use some mole grips or the like. Alternatively, cut the heads off, remove the rubbers, weld a nut on the remaining bolt shaft exposed. The heat from the welder will break the corrosion hold. Then simply unscrew them with a spanner/socket on the nut. 

Apologies, I should have been more specific. The “x” on the head of the bolt is stripped. I used a regular Philips instead of JIS. 
What do you think about either using a screw extractor, or cutting a flathead slot in the head?
I don’t have a welder, unfortunately 

Those screws tend to seize after 40 years.  Even with a JIS screwdriver, you won't get them out unless using an impact driver.  At this point, some vice grips should be able to remove the outermost screws, then try to spin the boot CCW, which often times cracks loose the inner screws.  If that doesn't work, then you have to try to get an impact driver on the screw.  Some long extensions should help you with that job.

I think i vould heat the alu with a mini torch flame if remember right the manual tells to use locktite on those screws so to losen you can heat them. That old alu can break if you use too much force. And be careful not using the mini torch with gasoline nearby !