for 1991 ford mustang lx convertable
If you have bought after market ones there should be instructions and if you are replacing the factory sub for uni-body convertible there should be matching holes. Since you are messing with the geometric of the car you shouldn't go blindly into this unless you have mucho knowledge. on the dirt track we weld everything together while making sure that the vehicle is sitting on four matching jack stands that ARE NOT under the suspension and that they are paired front with front and back with back preferably between the front and back axles to guaranty that the vehicle is still straight when we are done.
Being that your car is a convertible the effect gained by installing subframe connectors would be negligable.But if you want to do it any way I recomend having them welded in place as oposed to being bolted in.It's a fairly simple upgrade,start by supporting all four corners of the car with jack stands and MAKE VERY SURE THAT THE CAR IS AS LEVEL AS YOU CAN MAKE IT BOTH FRONT TO BACK AND SIDE TO SIDE ( DOING THIS PROJECT ON A FLAT CONCRETE FLOOR WILL GO A LONG WAY IN DOING THIS) then with a handheld grinder remove any crud or rust from the ends of the exsisting front and rear subframes then do the same to the inner surface of the connecters and then fit them into place MAKING SURE THAT THEY ARE EVEN FROM FRONT TO REAR ON THE SUBFRAMES YOU DON'T WANT ONE SUBFRAME MORE SUPPORTED THAN THE OTHER ONE.Then put a couple of tack welds on each joint to hold it in place and then finish welding the connector into place (one point do not weld the entire outer or inner side in one continuos weld as you risk over heating the metal on both the connector and the subframe but rather make many short welds wher the connector meets the floor of the car about a inch to two inches long each then switch to the other side to give the metal time to cool.After all the welding is complete and the metal is completly cooled then apply some rubberised undercoating (any parts store should sell it in a spray can) to the connector and the joints where they meet the subframes to prevent any rusting and you should be all set.
