well yes and no. physically the engine will fit. however you will have to make new engine mounting points. also the gearbox would need to be changed.
with the mk1 panda never having the FIRE engine fit to it, it sadly never came with the bolt holes to fit the FIRE line of engines in.
its doable if you can weld however. also remember that the gearbox would also have to come from a FIRE engine.
also is worth noting that the drive shafts are not as long as say a Punto or other wider Fiat.
i have with great success engine swapped a mk2 4x4 panda from the original carbed 999cc fire to the multi point injection 1242cc fire as its an absolute drop in replacement only requiring slight electrical work and a in line fuel pump adding.
sadly i am not fully in the know with pushrod engines. i have had a Seat Marbella with the 903cc engine and it was very nice. i know its pretty much identical to the 899cc engine which for you would be a direct swap with a bit of wiring work and again a in line fuel pump.
no messing with gearboxes as the engine will just bolt strait up.
Kolza i think would be more help than me on the 903cc push rod engine types... maybe?