Trans cooler recommendations........

Hmmmm.....I like that one even better. I was thinking of going 6AN because it was closer to the original (or slightly larger) line size - would the 1/2" inlet be too much of a difference in size? Would going to an 8AN line be better? I have no idea of the flow/volume/pressure of the trans lines....

If you want to run -6 lines, all you need is the appropriate adapter fitting(s).

Universal Fittings - AN to NPT Fitting - 1/2 in. NPT Fitting Size 1 (application) -6 AN Fitting Size 2 (application) - Straight Fitting Angle - adapter-fittings

I would day -8 line would be way overkill.