basic diamond frames for a pipefitter, should be straightforward.
the lugs, like plumbing elbows, are just not at 90 degree angles..

I still have the frame I built in the mid 70's, stamped lugs,
cast BB shell and fork crown.

use common 72, 73 degree head/seat tube slope and things go together
with out much drama.

1st frame stick with heat tolerant steel alloys, I got a Columbus Aelle tube set.