Replacing 90 degree crt with 70

[ppppenguin]

The first thought is that it won't fit in the cabinet. A 70 degree tube is longer than a 90 degree and will stick out of the back. Otherwise it may work, though it will be overscanned and linearity may be poor.

Compare the data sheets and check:

Same basic electrode structure?
Same neck diameter?
Same focus method? (magnetic or electostatic. The AW53-80 is electrostatic)
Same heater voltage and current? (this can be accommodated if necessary)
Is EHT voltage rating sufficient?

https://frank.pocnet.net/sheets/127/2/21YP4.pdf
https://frank.pocnet.net/sheets/030/a/AW43-80.pdf

Since the AW53-80 was relatively common in the UK it may be better to post on a UK based forum.