Here is a general drawing that is not correct for one specific model. Unless you have a Hydra-Matic transmission, the Suburban brake lines are the same as other 1954 1/2 ton bake lines. Please note that 1/2 ton brake lines/hoses were not the same from 1947-1955st.
Unless you are not correctly/completely describing your mis-matched parts, it looks like Inline Tube is BSing you.
1. You state that the ends on the brake line do not fit/match the ends on the flex lines/hoses?
2. You state that you bought both the lines and hoses from Inline Tube?
The only logical conclusion is that Inline Tube is wrong.
If you send me a private message and include your phone number, I'd be pleased to discuss this with you. If you want, I will then call Inline Tubes.
