Please please please photos of your Torana
Considering you live in Perth with no hills (I've not been there but its pretty flat eh?) I'd consider running the standard engine. Maybe play around with it and spec it up a little to get say 70bhp. That would make for a cheap to run nippy rare classic. Cant be that many original HB Toranas about?
Yeah I know I cant talk.. having V6'd my first HB. But its original engine was shagged plus we have some serious hills here.
Be aware that sticking anything remotely heavy in the front of an HB does really upset that nice light original handling.
The engine Id love to fit to my wagon if the original does not pan out would be a twin cam nissan 1200cc. Super light, super thrifty and nippy enough. Or Datsun engines drop in nicely.