starter question, need more power Options

[freezing14]

Ok i get ready to start by newly rebuilt 1.7 bored to 1.8 with ss valve and upgraded spring with swivell foot adjuster,, the engine crank ok without the spark plug, but the starter is not strong enough to crank with the plugs on , I check the the crack was free reving by removing all the rocker just to make sure and it cranks just fine with the plugs, but if I add the rocker which also turn freely on the shaft, it cannot crank, those dawn bugger spring are stiff,, now i know i need a new starter, but like most of you I am cheap , so what are my options,, bus starter,911 starter,, can you upgrade the 914 core to give it more torque, keep the core, cheaper,, or is it just because it is a 30 year old starter,, By the way i tried 2 starter, a new battery, the one from My S4 and the car is a 72 1.7 d-jet