Although the PUT and INPUT functions are valid in the DATA step, the PUTN, PUTC, INPUTN, and INPUTC functions are more widely supported. Since you want to use Numeric formats, use PUTN and INPUTN. (You chould use the C versions for Character formats.)
proc iml;
x="27mar2020"d;
t = putn(x,"yymmn6.");
y = inputn(t, "6.");
print t, y;
/* or next the function calls */
y=inputn(putn(x,"yymmn6."),"6.");
print y;