686 coolant reservoir exploded need advice

Hello,

I have been having issues with head gaskets. I put a OEM on. I didn’t realize the fan wasn’t working and I think it got too hot and blew the head gasket letting coolant into the combustion chamber. Took the plug out blew and little coolant that was in there out. Got the fan working but now my coolant reservoir exploded when I was out for a test ride. So I’m guessing it’s letting pressure through the opposite way now. It exploded right when I got on it a little bit. I’m guessing the head gasket is toast. I think I need a Cometic head gasket that is thicker. What would be a good size to replace it with? I have had several issues with the standard thickness gasket. Please let me know what size I should get Cometic Has a million sizes to choose from?
Here are my mods:
JE pro series 102+2 mm 10.0:1
686 big bore
Run premium fuel with Lucas fuel additive
Lucas 5W-50 oil
Marine grade Lucas grease
Engine ice coolant
Pro X #25 pilot jets
Dynojet needles & 148/150 mains
Needle valve set
Vito’s fuel screws
Big gun muffler
Tarzon rear brake rotor
Throttle master extension
AS3 performance silicone coolant hoses and clamps
Frame skid plate
Oversized aluminum oil reservoir
Front and rear aluminum pull bars
ASV F2 shorty clutch and brake levers with dust covers
Skat trac 20-10-10 paddle tires
21-7-10 tires
Rear swing arm extension +5
Pro taper handle bars
Pro taper stealth bar pad
Mod quad polished aluminum handle bar cover
XFR skid guard
7 inch LED slim light bar
Outerwear’s air box cover
-1 +2 sprocket gearing
D.I.D 520VO O-ring 108 link chain
Vito’s aluminum gas cap
Dirt skin Shock covers
K&N air filter and crankcase breather
No air box
Parking brake removed
H6M LED head lights
Aluminum throttle assembly