Rushlush, that Harrison bow is junk. The best thing you can do is box it up and send it to me for disposal. OK..Ok...I'll give you $20 for it!!
Just kidding, Jack builds a great, great bow!!! Jack did also have an arrow building company that built wood shafts out of Sitka Spruce trees (very abundant here in Alaska). I am betting that Jack would suggest shooting wooden arrows out of your bow, but it should be cut close enough to center that any properly spined carbon or aluminum will work.
I prefer would arrows out of my trad bows. I am currently shooting compressed cedars which are tough and heavy.
I would suggest buying an arrow and testing it to see what the bow likes!! But, I think 75-80# is too heavy. You should only be pulling 58# at 27", so I would go with 65-70# spine.
Good luck, have fun....AkBillyBow