I have a 1985 L series wagon with a motor that has the typical ticking, but just keeps on going, and wanting to put it into a 1992 Brumby.

Jordan.This requires a gearbox adaptor to use the current gearbox or modified driveshafts to use a mtaching gearbox. You'll also need modified or custom engine and/or gearbox cross members. Then there is the decision of using a matching or after market ECU and the wiring there of. Also if you choose a DOHC engine you may need to modify your chasis rails which I have been told the RTA is cracking down on big time lately.
In NSW anything upto a non turbo EJ20 can be fitted and complianced without further modifications.