I think for 2103 dont need conversation for 1700 niva engine,because old original 1500 engines is best quality than latest lada production aprox three times!
In our area every serious engine tuner looking for older engine units for tune.
For good 2103 engine You need make racing head from original-instal bigger walves,ported,polished with bronze walve guides,race springs,titanium retainersadjustable camgear of course-good one camshaft,forged pistons,modifide chain tension mechanism ,done well balancing,slightly lightened flywheel with stronger clutch,exaust manifold,inlet with 45 mm webers,electronic ignition-and You have very good engine.
Conect it with four speed close ratio gearbox& plate type lsd with 4,7 final drive and You have long life rally gun!