Master cylinder replacement woes

Thanks yall. Original idea was to use the original T by removing the rear line and connecting a new 3/16 line to the MC with a coupler, which I now have, removing the 1/4 line from the old MC and plugging it, which I did, then connect the other side of the MC to the vacated 3/16 on the T vacated by the rear line.
Didnt go as planned as you can tell!
I am dithering on the idea to just replace the old rear line, its nearly 50 years old but for one it has the wound wire around it, can one safely replace this with a steel line without the wound wire?
Thanks for the quick reply, thought I would have this converted over the weekend, ;-)
Right!