Go 1J or 2J and be done with it. The initial cost to do the swap is a bit more, but it is well worth it if you plan to keep the car for any length of time. I have been on this forum for nearly five years, and I can’t begin to count the number of threads on 7M rod knock and BHGs. Thread after thread of owners singing the same sad song. Yes, there are a lot of people that buy these cars because they are "turbo" and "cheap". This new illustrious and misguided MKIII owner then compounds the problem by buying crap parts, cutting corners, turning up the boost, and then stares in wonder as to why the motor blew. However, there are many who spend a substantial amount on the rebuild and don't cut any corners that inevitably end up with the same sad rod knock or BHG song.
There are numerous threads on the JZ vs. 7M debate so search and read to your heart’s content on the arguments for and against the various motors. I do challenge you to go back and research to find how many JZ owners (1J, 2J, or 2J NA-T) develop rod knock or BHG’s compared to those who were loyal to the 7M. Yes, there are JZ engine failures, but I am sure the numbers pale in comparison to 7M builds. Most of these JZ motors are pulled from Japanese junkyards, shipped to the United States, and then dropped into a MKIII, SC300, or 240SX without any refresh at all . They are then driven hard and beat on daily.
Once the swap is done, cost of ownership is very affordable. In the event that the motor does fail, it is dirt cheap to replace it. You can get a 1J long block for $700-$800, a 2JZ-GTE Aristo for $1400, and a 2JZ-GE for $400. Unless you are looking to build a monster dyno queen or drag car, a junkyard JZ longblock will give you a reliable 400-600 rwhp all day long with supporting accessories.
I wish you the best. You won’t be the first and certainly won’t be the last disheartened owner to abandon the MKIII due to 7M engine failure. It is obvious that you love the car. Do what Toyota did in 1991 and give the Supra the engine it should have had all along.
Chris