Pre 1950s rides of LFGSS: old bikes, vintage rats, classic lightweights

Put it against a straight edge....see if it has any bendage.

Can you get the forks out and check that the 2 little 'flaps' of the T cut have not been bent in that prevents your stem shaft from getting any further in? Might be just millimetric, might not.

it has, very slight, but i think it would be enough to stop it going in.

i tried the quill stem expander bolt trick, but no luck so far.