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...So 73+ transmissions don't generally need welded 3rd/4th, but benefit from the stronger 002 bus coarse tooth gears?

Correct. The 002 type gears in a 73 and later type 1 gearbox have their synchro cones brazed to the gear instead of being a simple press fit like 72 and earlier gears.
However, brazing is not as strong as the electron beam welding that Bus gears get. Also, Bus gears are never super fine tooth like Beetle gears. For all out strength, use Bus 3rds and 4ths from a 72 or later Bus 'box in your Type 1 gearbox that uses 002 type gears.