Sorry for the no-reply. It's been a whirlwind. Getting a new job, and working like mad to finish my enfield build. Making a custom seat tonight.
For my contacts I got these little connector things that slide right over the little tabs on that battery I bought. They sell them at home depot, or probably any store. It's the female connectors you want, and I think they come in 3 main sizes, based on gauge of your wire you're connecting them to. I got the biggest ones they had but could've gone with smaller ones. I ended up cutting off my stock battery connectors (the screw-on ones) and wiring straight into these little tabs. Works great so far. No solder required... just taped it up. You need to crimp the little connector things to make them clamp onto the wire. I didn't have crimpers so I used needlenose pliers... it worked but i imagine having the real tool would've made things easier.
I have almost 500 miles on it since doing this mod and it seems to hold up well.
I attached an image of the crimp connectors I used... mine were yellow. They friction fit very snugly to the little metal tabs on my battery... you just tug hard when you want to get them off.
Not sure any of this helps since you're looking to keep the stock connectors, but it's at least what worked for me. Small, efficient, and it works. Space saving, and looks good.