I have a lead on an 8 3/4 rear end housing in good shape without the hard brake lines. Are the hard brake lines on a 7 1/4 E-body housing the same as the brake lines on an 8 3/4 ?
They will be similar in length but the vent tube that holds the Tee at the end of the flex line my be in a different place , they may be workable but are nt hard to make if needed .
Brake lines are inexpensive and a safety must.
I would at this point since you will need to bleed the entire system anyway, order a new set of brake lines and hose, flush everything out first and install new ones.
Safety first.