Drilling the underside of a Steel Lintol

[bricky48not]

Hi There, I am looking into installing 'Removable Security Bars' in a 4' x 3' window in my house. The Security Bar arrangement that I am interested in have metal strips on the inside of the window that retain the metal Bars. One which has holes to feed the Bars in and the other one to fix/lock the Bar in. The fixings can be on the sides or Top and Bottom. The natural method to me would have them on the top and bottom for the shorter vertical distance for the bars. But that would mean attaching the top fixing into a Catnic Steel Lintol. Is this common?
If I mount them on the sides of the window then the fixings would be fastened into the inside leaf which is 6 inch Thermalite Blockwork which is pretty soft.
(The bottom strip would also be fastened into the 6inch inner leaf also).
If the side fixing will be the way to install it, what is the recommended fixing for fastening the strips into the Thermalite Blocks please.
Many Thanks.

 

[jj4091]

You could use these to fix to your Catnic https://www.screwfix.com/c/screws-nails-fixings/self-tapping-drilling-screws/cat840058

 

[bricky48not]

Thank you jj, I was a bit concerned about drilling in to it because of comments I've seen (not on here).
Much Appreciated.

 

[noseall]

I was a bit concerned about drilling in to it

No dramas. Lintel manu's expect it.