Sway Bar Bushings NOS 3986486 (Fitment??)
 

I have NOS GM Rubber Bushing(s) 3986486 that
measure roughly 13/13 ID 1.5 inch Long 1.150 OD Approx .180 wall

I ran that on Google with No Good Answer....

Anybody reading have old parts book with applications

Seems like a very large Rear Sway Bar Bushing unless this is
"something else"

3986486 - 1970-1973 Firebird TA rear stabilizer shaft.