Brake booster/master question 3/4 to 1/2??

[Furno68C20]

I have a 67 1/2 ton that has manual brakes. The master cylinder is filled with debris and no fluid since its been sitting for a number of years. This truck is Drum/drum

I have a 68 3/4 ton that i just put disc conversion on, it was previously Drum/drum with power breaks. This master and booster is in good working condition.

My question is can i put 3/4 power brake set on the 1/2? I see that the booster extends the master cyl / distribution valve brake line ports forward. What would be the best solution here..new lines? just extend the lines? any size difference in brake lines?

here are a few pictures.

1/2 ton on the left 3/4 ton right.

What is that rubber washer? does that go between the master and booster?

sorry about the side way picture.

Thanks in advance!