STEP 3: Located the rear studs.
This is the most difficult part in my opinion. Here is where you need your 7" long bolts of whatever pitch you choose, and the plate steel. And welder. And other things mentioned.
A. Before going forward, you
need to add a 1/2" spacer to the rear of the subframe around the bolt holes. Could be just a hair more than that, but 1/2" steel is easier to find. A round piece, two cut square tubes, whatever. I welded mine. You need to space the rear of the subframe off the car by that 1/2" (or slightly slightly more) to align the frame correctly. This compensates for differences in the chassis.
B. Next, start mocking up the subframe to the car by using the front studs. Best way is to remove the steering rack, hubs, etc to make it as light as possible. I usually leave the sway bar since you need to clearance something here shortly. Also, it serves as a nice handle.
C. You'll notice the pinch seam prevents the subframe from sitting flush. You will have to clearance for the sway bar, the front stud area and the rear stud area like the example below. I leave how much to clearnace to you, but do not overcut, and try to maintain the cut on the x-axis so you have a flush surface and no points to deflect the subframe. I usually weld any stray penetrations and grind / file smooth.
D. Using something to mark the proposed location of the new rear stub through the subframe. Sharpie marker works rather well. Then using a pin punch, mark the center for drilling. You need to mirror this to the top of the frame as well. Carefully measure and translate this marking to the top of the frame. I use a combination of a metal engineering rule, a square, and check several times. Then mark the top.
E. Now using the appropriate set of drill bits, drill your holes from the bottom and the top (probably independantly) so you can have a passage all the way through. It comes very close, borderline engaging the frame insert to the unused steering attachment points.
F. On your steel reinforcement plates, measure and mark the distance off the the side of plate so that with a hole of the same size drilled through it, it can fit snug to the frame, but align through the holes you have drilled. This spreads the load and prevents the bolt from pulled through or deforming the sheet metal.
G. Drop the bolts through and tighen the frame up proper. Then weld up the plates and bolts. Your mounts are now done.
H. Paint for rust protection as needed.
