Sparking Battery & Starter Issue

Evening all, I did do a search of the forums but saw nothing that matched my issue...

I recently bought a 1976 280Z. It's in relatively decent shape with no significant rust, an incredibly clean (original!) interior, and is mostly mechanically sound.

The only issue I had when I first got it home was a slow starter. When I turned the key it would pause a moment then the starter would chug a few times before the motor fired up. Once running it idles great, drives great, shifts, etc. All electronics (except the clock) also function 100%.

The battery was 4.5 years old and the car had not been driven a lot over the past few years so I went and got a new one. When installing it, I went positive first then negative. When I connected the negative side it sparked like crazy and smoke came from the fusible link. I've changed enough car batteries in my lifetime to recognize this wasn't normal and in my research I found that this might be due to the starter going bad? Is there any validity to this? If so, when I swap the starter will it still spark like crazy during the initial connection?

Also, I've seen some fusible link upgrades, anyone have experience with those and their value?

I will add, that the majority of my wrenching experience is on cars made post 1984 (and that usually involved a laptop and fuel maps...), so I'm probably approaching my new Z with more caution than usual.