I gather you want to shoot LSWC bullets in 38 Special cases that surpass or duplicate 357 Magnum velocities? About the easiest way I can think of is start with hot 38 +P and work up. Limited case capacity and resulting pressures comes to mind when trying to put 357 loads in 38 special brass. But, I wouldn't try because if I want 357 ballistics, I'll shoot 357 Magnums, brass and all (and if I want more power, I'll go with my .44 Mag.), and I can get 357 Mag. once fired brass fairly easily for around $15 per 100.
My Anchor is holding fast!
I've learned how to stand on my own two knees...