Shapechange: Spell Save DC and Spell Attack Bonus

The Spell:

Shapechange: 

You shape-shift into another creature for the duration or until you take a Magic action to shape-shift into a different eligible form. The new form must be of a creature that has a Challenge Rating no higher than your level or Challenge Rating. You must have seen the sort of creature before, and it can’t be a Construct or an Undead.

When you cast the spell, you gain a number of Temporary Hit Points equal to the Hit Points of the first form into which you shape-shift. These Temporary Hit Points vanish if any remain when the spell ends.

Your game statistics are replaced by the stat block of the chosen form, but you retain your creature type; alignment; personality; Intelligence, Wisdom, and Charisma scores; Hit Points; Hit Point Dice; proficiencies; and ability to communicate. If you have the Spellcasting feature, you retain it too.

Upon shape-shifting, you determine whether your equipment drops to the ground or changes in size and shape to fit the new form while you’re in it.

The Question: If my level 17 Druid with 10 Int and 10 Cha uses Shapechange to turn into an Adult Gold Dragon, retaining these scores, what would be the spell attack bonus and spell save DC?

The statblock reads: 

Spellcasting. The dragon casts one of the following spells, requiring no Material components and using Charisma as the spellcasting ability (spell save DC 21, +13 to hit with spell attacks)

My understanding would be that my Druid casts Guiding Bolt and Zone of Truth from the Dragon's Spellcasting feature not with +13 and DC 21, but with +6 to hit and DC 14 based on having a +0 modifier and a +6 Proficiency Bonus. Is this correct?

Added wrinkle: My druid has an amulet that grants +2 Spell Attacks and Spell Save DC. If I choose that it changes in size and shape to fit the new form, its bonuses should still apply and lead to +8 and DC 16 accordingly, yes?

Please note that this is just the way I rule it, but I know other people do it differently. See, for example, page 2 of Does Shapechange Retain Your Spellcasting or the Monster's?

And well, from the same thread, this is my opinion:

Quote from Tarod_ >>

Quote from R3sistance >>

Quote from Plaguescarred >>

Yeah keeping both Spellcasting would definitly give more options but would also create issues in that you potentially have two spellcasting ability, attack & spell save DC etc...

I would also welcome a Sage Advice Q&A  on this topic.

I don't see that as a major issue, if a Wizard multiclasses into a Cleric, they would have separate spellcasting abilitiy attacks and spell save DCs between the two classes, so using shape change would be no different, the creature's spells would use the creatures spellcasting ability attack & DC while the caster's own class spells would use their spellcasting ability modifier for attack and DC.

 That's also my understanding. You follow the monster's stat block when you use one of its actions, like a melee or ranged attack, or a spell it has.

EDIT: similar to when you wild shape into a Beast, where you use directly the information from the stat block if you use those attacks.

Quote from Disil >>

[...] Added wrinkle: My druid has an amulet that grants +2 Spell Attacks and Spell Save DC. If I choose that it changes in size and shape to fit the new form, its bonuses should still apply and lead to +8 and DC 16 accordingly, yes?

 Regardless of how you rule the first question, I'd say adding the bonuses is right.