I know a little something about this question..
Heres what i've found so far. The easiest thing in my humble opinion is to take your toyota pressure line and cut the double flare off of the steel line so that you can remove the nut and do the same to the chevy line then just put the toyota nut back on the chevy line and reflare it.. Now your set to go..
The other option i've seen is to buy an adapter from Downey which threads into the toyota gear box and converts it to a standard fitting so that you can have a custom line made up at any local hydraulics shop.. Dont even bother trying to have the hydraulics shop match up the metric gear box fitting because its a given that they will not have what you need..
As for the return line, its just a low pressure barbed fitting that you can just put the hose on and clamp it down and you'll be good to go..
Like I said my personal preference is to put the toyota nut on the chevy line and reflare.. I'll let you know how it works out in just a few days seeing as how i'm just about to bolt in the 4.3.. Hope that all made sense and is in some way helpfull to you..