I just completed the same conversion. I don't think it's wise to run R134 through an R12 system due to contamination, but you can flush out the condenser. The evaporator? I did not pull the dash for that. Everything else I changed.
Don't forget the expansion valve under the dash. Be careful, if you twist it off you'll have to pull the dash out. You need two large wrenches and patience.
I got it from Nostalgic AC parts. SKU 14-9875. $20.00.
Also, be aware of your connections. The original system uses flare fittings, not the best for R134 as it may leak out faster. You might want to convert to O ring fittings.
The Expansion valve I listed is for flare fitting, but they have O ring too, plus any adapters you might need.
There are a lot of Sanden knockoffs. I spent hours searching for authenticity through the heaps of probable Chinese junk. I finally decided on Summit number RSS-58033 (SD508). Who knows.
Finally, I believe the bracket is Pantera specific.
That's all I have.