By the mid to late 70's we started to make the transmissions shift smoother and smoother without trying to sacrifice durability. The lock up versus non-l/u units really only differ from the earlier units by reducing the front clutch friction count down to clean up the 2/3 shift and smooth out reverse engagement. Some valve body orifice and ball changes to slow the rear clutch apply and some other tweaks. If you are changing the trans just to make it shift better you can avoid that by a good shift kit, 4 disc front clutch, lose the wavy snap ring in the front clutch and go flat, block the accumulator and block the lockup module spring to prevent lockup ( if you don't want lockup ). Better yet - if you want to drive in lockup and have control of it - install a late model electric lockup valve body. Drill the case like you would do for a trans brake for the bulkhead connector and run a wire to the dash for a switch. You can spend some time to make that automatic if you wish - depends on your inclination on auto versus manual control.