What all should i replace while replacing the head gasket?

Hello, The full gasket kit is great, at 190k I would probably flush the oil and coolant before the repair, inspect the valvetrain for wear, especially the rocker seats, and consider replacing the timing set while it is all apart (not really necessary in most cases unless you find wear or damage). Don't attempt to clean the exhaust manifold out, it will just cause your catalytic converter to plug up, but cleaning the exhaust ports on the head is en excellent idea. Don't clean the carbon off the tops of the pistons with any sort of abrasive wheel, use something that won't damage the surface of the piston, and ensure the pistons are at TDC before cleaning them so you don't scar the walls. After that, standard maintenance as outlined in your owner's manual.