If you do the math, assume 20 mins from wheels down to commencing disembarking, so this takes you to 6.10. Assuming flight is on time and no holding at heathrow,
You then need to count back, you need to be at the aer lingus desk no later than 8.45, probably 8. 30 to be safe as the computers will shut down check in at 8.45. Assume twenty mins to get between terminals ie to get out of one, walk or catch train, get to check in desk, especially if unfamiliar with layout.. So you want to be be picking your bag up at 8.10 latest.
This gives you two hours to disembark, get through immigration and collect luggage. Doable, yes, absolutely, the big questions are how long will the queue be at immigration that day and will my inbound flight be on time.
So yes, it carries a risk and you need to have a back up plan in case something goes wrong, which sometimes it does.