<VV> 1965 model tail light wiring?

[Arlette Pat & Carl Kelsen]

G’day everyone,
I feel like a  complete ‘fool’ asking for advice about the following as it should be simple to resolve but here I go....

I have a Clarks Corvair supplied rear tail light wiring harness, which from all account appears identical to one its replacing.  I have NOS tail lamp lenes which are attached to NOS backing plates. All is in perfect condition.

However, I am finding the globe holders very difficult to ‘push’ into the backing plates. Interestingly the reversing light globes holders push in without difficulty but the stop / tail light holders simply refuse to push into place no matter how hard I push, turn or position them on to the backing plates.

I have tried and tried to get them to fit but am concerned that if I push any harder I will damage / bend some components.

Is it that these parts are simply very hard to fit when new and I should I just keep trying or am I doing something wrong?
Regards from Australia
Carl Kelsen
RHD 1965 Monza convertible