Does this cruising mean long distance (where you would eventually be thinking about decent fuel economy), or just cruising around town the local countryside? (I.e., you're not much concerned about fuel economy but want to be able to romp on it and feel the g's...)
If you are not attached to any era of 360, then I would start with the Magnum; better compression ratios 'out of the box' (Makes for a wider torque band). And 1.6 rocker ratios... better lift-to-duration ratios.
Look at a lot of topics here and notice all the discussion on head flow and flow bench work, and porting. If you are gonna spend money and/or work, spend it on heads. Flow is where the HP is. 400 HP is pretty much available bolt-together parts in this day and age.....which is where the budget questions flow from.
Next is compression ratio; that makes the torque and if you do it right, the torque band is wide and starts at lower RPMs and that is important for a street cruiser, which lives in the lower RPM bands. More budget questions from that... and so starting with Magnum gives you a leg up on getting a better CR for street use without going overboard.