Well, I guess that depends.
My 12" is a -756 out if a truck.
The 606, to the best of my knowledge only works with the 10.5 inch clutch.
The 697 works with the 11 inch clutch.
I have never seen a 10.5 inch flywheel for 454, sure, if it was a 396-402-427 you could just use a small block flywheel, maybe add a balance weight from a 383/400 SBC crank to make it work with a 454.
So, if you're running a small motor, with a small flywheel...no issues, other than you would have to buy another clutch.
The 486 could be modified, and, you already have the magic fork.
Measure the front bearing reatiner hole, there are two sizes seems like:
4-11/16" (car)
5-1/8" (truck).
That is the hole the front of the transmission sets in.
I took a collection to have welded for the conversion:
Two 383/606 -10.5"
One 697 car 11"
One BOP Buick-Olds-Pontiac
One 756 12" Chevy with the 5-1'8 hole (I have a Saginaw 3 speed car trans it fits *most likey from a truck, three speed on the column*, the front bearing retainer may fit a for speed never checked, the bell housing will fit my A883 OD four speed trans though).
So, yes it can be modified...
I figure some of mine will be done on Friday or so.
Ill take some pics and post them
Did that answer your question?