Two comments.

a) Ryanair passengers are not permitted to transfer airside at Gatwick per airline request, even if only traveling with hand luggage and EU documents. GAL Security will deny passage to those holding Ryanair onward boarding passes and redirect through immigration.

b) The IEX flight on Sundays operates using an aircraft that originates in Newark. In late-August, EWR has historically seen horrendous delays and ground stops. The flight will almost certainly be delayed at least 30-60 minutes into LGW.

You will not make the connection. Don't attempt it.