aussie 408 combo

IMO - that cam is a mistake. It will be torquey for sure - but it won't carry up anywhere near 6K. A "low rpm" 4" stroke engine needs something that would be mid-size for a normal factory stroke just to be mild. The Crane 302-2 hysdraulic is a favorite of mine. With deceent heads it will idle at 800, have 13" of vacuum at idle, and pull to 5500. It also gets decent gas mileage if you can keep your foot out of it. That one is 242/252 @ .050. The Howards is 219/225. If you want to stay with hydraulic roller Howards then I'd recommend either the 710831-08 or 711351-08.
IMO - the 1.6 rockers are a mistake especially given the valve springs needed for the lifters and lobe design. I think they will also limit the rpm capability of the camshaft.