From much experience stick to an un molested twin turbo, if you buy anything else you will have MAHOOSIVE problems selling it and probably end up breaking it down for spares, singles are just not selling and knowing your frequent change history i am sure you wont want a car that doesnt sell quick.
Make sure you also have documentation of recent rebuild and very recent (like within a week or two) compression readings and good history, also make sure this all ties up with the car you are buying. Also make sure these compression readings and rebuild have been carried out by a well respected specialist. Re-Worx, Hayward Rotary, Rx Motors, Powergains, WGT, Dragon Performance.
Plenty of info on fduk or mazdarotaryclub