Need advice on Oil Pump

The only time you really need the HD shaft is if you run the pressures really high like 80psi hot. As long as the pump pressure valve is working correctly it should blead off extra volume above the preset pressure. I personally have used the stock pump drive with HV pumps on my oval track race cars turning 7k plus and never broke one that's in 20 years of racing. I would run what you have and if the pressures are high when hot run a thiner oil. A little more oil running over them valve springs will help cool them and make them last longer.