Help me identify a screw head please

Hey Gang I was having a tough time deciding if this was one for this forum or the auto repair crew. I'm restoring this old commercial dough mixer. I have the unit largely broken down ready for blasting and refinishing. I'm down to the last four bolts that I need to remove. Here's the problem. The housing including the bowl lifter and strap locks are aluminum. The slot head screws/bolts are steel. I've used penetrating oil and impact drivers. These bolts wont budge. This thing was made in the 80's and those bolts haven't turned since. I was thinking to use a drag link socket on a breaker bar but I'm afraid I might just shear the head off. I'm also being told I can heat it but I'm not sure weather to heat the steel nut or the aluminum housing? I also have no idea how much heat to add. I don't want to damage the housing. Replacement parts are not available for this thing. I'm not sure if I can melt any of this with a garden variety propane soldering torch. If I do heat... do I allow it to full cool before attempting to remove it? And then how much force can one safely apply? I'm thinking since this are steel bolts in an aluminum housing this is a case of galvanic corrosion but I can't find anything useful out there on how to free it up. I'm hoping someone might have some clever suggestion as to how to free up these bolts without destroying anything? Thanks all! [img]https://cimg2.ibsrv.net/gimg/www.doityourselft.com-vbulletin/1125x1500/mixer1_dd8721fd0382b441d9606f4c47a0fda80c3c4ad5.jpg[/img] [img]https://cimg5.ibsrv.net/gimg/www.doityourselft.com-vbulletin/1125x1500/mixer2_a5080ed1ff49a0f13aa326cca05c70d74a35c0a5.jpg[/img] [img]https://cimg9.ibsrv.net/gimg/www.doityourselft.com-vbulletin/1106x1500/four_screws_fa4ab43372d123edf725631f6ba63e43fab1284a.jpg[/img]

Hi, I have 2 pair of Blum 170* hinges, they will snap off of the base plate fine, but will not snap back on, any one else experienced this? Geo 🇺🇸