These bean should blend OK.
I did a darker roast of the Harrar and also got the bitterness initially. It will also need a longer rest period than the Peru. It wasnt that good straight out of the Baby for me but much better a week later.
I would roast the Harrar a little lighter than the Peru but its also about your taste. Your mileage may vary.
Get some more Peru. This is a always good bean to have in your stash while stocks last. Reliable and easy to roast
Roast another batch of the Harrar two days before you roast the peru then try them in different proportions to see which blend works best.