Hi all and thanks for reading.
Hoping to get advice before I spend $$$ on the wrong parts.

3rd owner of '67 Conv which has a past I don't fully understand, but it has been restored.
Someone along the way pulled the smaller original motor and replaced it with a '68 400. (400 was rebuilt and runs flawlessly).
Original TH 350 was left in place, diff gears switched to 3.08 (I am told), and she drives like a 3.08 which fits my needs.
So .... she really needs a manual 4-speed Muncie m20 wide ratio if I'm to do the car right as her owner.

I have access to a beautifully rebuilt early '70 m20 wide ratio 10/27 spline, 661 case.
The '68-69 m20's I can find are shoddy or "unknown" rebuilds, but do have the 660 case that was age matching.
Will the '70 m20 bolt onto my '68 400 in my '67 frame ?
I know my TH350 cross member is a match for the m20.
Is the case difference between 660 and 661 is just going from male to female shift connectors ???
Planning on new flywheel, bell housing, clutch assembly, etc.

Was also told to get the Hust Comp shifter for '67-68 (to fit the "67 frame) .... and a shifter linkage kit for '69-70 Muncie to fit the '70 m20 with female shift posts. I am sure it will all fit together perfectly the first time ......

I know there are sure to be glitches to address with the swap and I am mixing years (it's already been done with the '68 400) but everything I read says the '70 Muncie m20 will work, and the wide ratio with a steep first gear is the correct match with my 3.08 diff.

Am I barking up the right tree with the "70 m20 as far as a compatible match to my '68 400 ?
I am only interested in an age appropriate 4-speed Muncie (not a newer transmission) to keep the era vibe correct for her.

Thanks for any advice or pitfalls that you have suffered through.