4l60e trannygoooonbybye
My reseach says if you have less than 650 tq you can stay 4l60, it'll run ya $2000 at Pro-Built in CA, $2200 at Level 10 in NJ, and $2650 in OH w/ Rossler. But now you need a $700-1000 anti-ballooning converter probably too.
I'd guess, even with all the small conversion parts, the 400 would be less, more work, but less. Some companies sell the entire kit you would need.

