Hello, although the request is from 11 months ago and the need for the manual still exists, I can say that it's very scarce. However, there is an alternative: downloading the manual for the Seat Panda or Marbella.
Regarding the engine, they are all the same engines with timing chains in 850, 903, and 1000 cc versions. The gearboxes are the same, except that the Terra, manufactured by the VAG group, has slight variations in the gear selector mechanism (particularly reverse) and its ignition system is static, meaning it uses a crankshaft position sensor, hence the elimination of the distributor.
There's a different procedure for assembling and disassembling the gearbox regarding the reverse shaft and idler gear, but explaining it would make the post much longer.
I hope this helps, even though it's late!