the helicoil will work, i've done it on a small block that i did'nt want to remove the box, just went with the kit that has the coil's and tap in it,used a air powered drillgun and a short bit, to get it square in the hole, screwed it in till it bottomed out on the converter with the some thread's floting in thin air. Just as long as the main threads are seated in the block it will hold.