I personally would never use a dual set. You should not contaminate a 134 system with 12 refrigerant and oil and vice versa.

A 2 stage vacuum pump is the way to go.

Your best bet would be to get Jims recovery machine. Having a recovery machine is THE way to go IMHO.

R12 is down in price now, so you can keep your SD on the good stuff for very little more money these days.

Have a great day,