havent installed into pinball machines but LOTS of experience using them with very small Lepai amplifiers. I've got many pairs (spares too) of the MCM paper/cloth woofers, I like building speaker cabs. lots dont know, 7-8 actual watts can be -very- loud with efficient drivers.
pinsider markmon wrote an "add a subwoofer" thread, he specifies MCM woofers too. a couple people kinda argued "it isnt a sub unless its active/separate/powered", maybe they just dont understand. when you replace a speaker that gives 87-89 db from 1 watt with one that can pump 94+, its easy twice as loud more bass etc, no real need for another amp.
"blue resistors"? would those be capacitors and coils (low pass) to cut out higher frequencies?
if so, yup, leave them in and swap the woofer to see what it has to say for itself. small difference of 4-ohm vs 8-ohm might change cutoff frequency a little/barely, if they are different. if they're actually resistors, like 8 ohm amp needing 2-3 ohms in series to a 4 ohm speaker, probably wouldnt need that connecting an 8-ohm voicecoil.
the MCM are really inexpensive but their sensitivity makes them great for lower wattage, worth a try especially if you dont want more stuff on the floor like an external powered sub.