Hey mate welcome along! gald you like the Forums.
The Escort has been around sice the late 60s, and in the UK was only just recently replaced by the Focus.
However there were 2 RWD versions, the MK1 from late 60s, the MK II from '75 till either 81 or 82 when it was replaced with a FWD version that remained relativly unchanged untill the late '98ish when the Focus was released.
In the US it was first introduced in '81, but it was not related to the UK version, instead it was a rebadged Mazda 323.
So you dont actualy have 1st gen escort.
Once you've got the basic bolt ons there is little more you can do, with out cracking the motor open and doing things like porting the head and adding cams or turbocharging.
A relativly easy swap would be the 1600cc DOHC Turbo from the Japanese 323, comes with 160hp and has some potential for more.
But also remember that much of a power increase will also require a serious brake upgrade.