no both ways are completely legal, its if you dump the refrigerant into the air that it makes it illegal. either one will work as for the drop in just google r12 direct drop in replacement and see what you can see

 

This has been awesome. I knew that if I turned to this site, I would be told exactly what I needed to know. Thank you Thank you Thank you to all of you that provided me with this info. After discussing it with the wife, I am going to wait on doing a project of this size. The truck is not my daily driver and I was wondering mostly about how big of a job this is. My plans are to get a 4 door f350 in the future, so I will save toward that and after I graduate college, I will have a lot more free time.

I think this will be valuable info for any future enthusiast who is looking at doing a project like this. Thanks again to everyone.

Bottom line-Yes it is possible, but time consuming. R12 conversions to 134 have been successful and as long as you find a good donor truck and with a little love, the system will work just fine. Use your cell phone for reference pics, replace the O-rings in the system, use the common sense you were born with and post you success on here for everyone to see!