No spark / No start

............Sigh...........Where do I start?

First, "sluggish cranking" you said. Of all the parts you threw at it does it crank good now? This is likely the first thing, because if you don't have a good battery/ cables/ starter, the ignition won't output good spark, either. So you have a "double hit".........the engine is cranking slowly, and the spark is poor. Either / both are a cause for poor/ no start

You have a multimeter? A second, good battery? test lamp? a couple/ few alligator jumper leads?

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Page teu, as Paul Harvey used to say

It is important to understand the ignition power circuit. The key provides direct battery power to the coil/ ignition during cranking, so that you get a better spark. If you say, are cranking it by jumpering the starter relay, YOU WILL NOT HAVE a strong spark, because the ignition will still be going through the ballast resistor.

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You NEED a meter and learn how to use it. You cannot "look" at cables/ clamps/ connections, and hope/ wish/ fantasize that they are good, bad, working, or not. VERY possible that a simple dirty cable clamp is all that is wrong here. Learn to use a meter!!!!

Put one probe of the meter DIRECTLY onto the battery PLUS post. Stab the other onto the clamp. jumper the relay and crank the engine, and read the meter. Should read almost zero, the lower the better. This shows you have NO voltage drop across the clamp. Now leave the meter on the post, move down to the starter stud. Crank it again. Should only have maybe, 3.--.4V (4/10 of one volt) or LESS across the cable.

Do same test on the NEG cable.

Now double check your test. Stab the probes into the battery posts Jumper the starter relay and read the meter. NOTE the voltage. You need MINIMUM 10.5V the more the better

Now move the meter leads----clip them to a ground on the block (such as carb stud) and to the starter stud. Crank the motor, read the meter. Should only be maybe......3--.5V max difference between the battery reading and this reading. Again, you want MINIMUM 10V better 10.5 or more