get the brake lines away from the headers i think thats is the brake deal. make some alumimnum heat sheilds leave some are gap for a heat boundary for the brake line with out the inner fenders in the heat may be getting push down and not out down on the lines. i have built header for small block S10 and the line on the frame get close on the drive side keep the brake lines at least 3inch or more from any header tub the master could be getting hot heat will rise to. but i would work on the line the heat may not be getting out were you think try a house fan in front of your S10 and you can find were the air is moving put a piece of yarn on a stick and move it to find the path of air movement