I'm inclined to think that the age of the thin aluminum is the primary cause of failure, since aluminum will work harden and crack.
It may be better to install an evaporator that is rated for the R134 pressure as well...
Obsolete air will supply one at $299.99 with free shipping to Niagara Falls NY where I have a 24/7 parcel service. It's 40 minutes away.
That's the best price I found, and it's similar to prices for other old cars.
I thought I'd get more responses, since A/C particularly in the southern US is needed way more than up here in Canada.
I haven't found any local shops that custom make or adapt evaporators. My A/C mechanic friends don't have any sources either.
[This message has been edited by David Hambleton (edited 05-14-2017).]