Overdrive Options

I'm just pointing this out and yes I would do this before you ask. Okay if you are willing to cut the tranny tunnel (no a ding with a hammer or cut a small section of brace for the 200R4) I talking the major surgery to install the 4l60/4l80, why limit yourself to the 4 speed auto? I'd opt to install a 6 speed auto and deal with the extra work needed. Really it's not the much more work to gain a double overdrive. I'm just saying that's all.