By placing fossils in a CT scanner, and taking over 3,000 X-rays from different angles, the scientists were able to create 2,000 slices showing the creatures in cross-section.
From these slices, the researchers created 3D digital reconstructions of the fossils which allowed them to learn more about their lifestyle, biology and diet.
One of the insects, characterised by a large number of sharp spines, is a species and genus which no longer exists.
The other is an early predecessor of one of the great survivors of the insect world, the cockroach, and is one of the best preserved examples of this age ever seen by insect palaeontologists.
Writing in PLoS One journal, the University of Manchester scientists said that judging from its "well preserved mouthparts" it survived by eating rotting litter from the forest floor.
Both are members of a group called the Polyneoptera - which includes roaches, mantises, crickets, grasshoppers and earwigs.
However, analysing the exact relationships of the insects would be difficult to work out said Russell Garwood because insects have a habit of dramatically changing appearance as they develop.
"The most dramatic change is seen in insects like butterflies, which change from a larva, to chrysalis, to adult," said Dr Garwood, co-author with Professor Philip Withers of the report.
"But relatively few people look to the fossils try and work out how such a life cycle may have evolved.
"We are hoping that work like this will allow us to better understand the biology and development of these early insects, and how major innovations may have come about.
"Around this time a number of early 'amphibians' were insectivores - they lived by eating a lot of insects.
"The spiny creature was a sitting duck, as it couldn't fly, so the spines probably made it less palatable. It is bizarre - as far as we're aware, quite unlike any members of the Polyneoptera alive today.
"The roach nymph is much like modern day cockroaches - although it isn't a "true" cockroach, as it may well predate the split between true cockroaches and their sister group, the mantises."
"This is very much a first step, and I'll be spending the next few years looking at other fossil insects to build on this work."