Just wanted to report back because of iso boredom.
Ended up getting the spare motor built, standard crank, aftermarket H beam rods, 1mm oversized dished pistons and your usual ARP bolts, fresh seals, etc. Got machine work done, bearings to suit from machine shop so it was just a matter of slapping it all together at home. Was going to go flat top pistons but supply and concerns around detonation with stock cams, i decided it wasn't worth the effort.
Before Victoria/Melbourne went into our first lockdown, I managed to get the motor finished and installed. Did a few drives to run the motor in and what can I say, even standard build, the motor has so much more torque than the old motor.
Blows less smoke, mid range pickup is amazing. This was literally no changes to carbs or cams as these were swapped out and over into the new motor.
Would be interesting to dyno this motor and see what power it makes now after run in. To answer my own question of whether it was worth it, with my goal, this was enough. More than enough power to blast through the hills or cruise through it in 4th gear.
The power drops off dramatically from around 5krpm though (so did old motor), so I'm currently looking into a new cam to open it up a bit. A 72 with high lift (which will require new springs and retainers) is looking like the choice at the moment as I don't intend on revving it any higher than 6.5krpm.
Also got the spare flywheel machined and lightened too but didn't install it as it's a 240mm item while the HD clutch I had and transferred over was only a 225mm. Will hopefully get this in at some point.