so, i have an old threaded free wheel roadbike with horizontal drop outs, but it has a one piece crank (ashtabula)

am i correct in thinking that i can replace the 1 piece crank with a 3 piece crank if i put in some adapters to fill the extra large hole that remains in the frame?

i am thinking that i can run a 1/8 chain with 16:42 gearing onto a bmx crankset, to keep the chainline tight.

does a 42 tooth chain ring on a bmx crankset with 1/8 chain onto a 16 tooth rear sprocket seem like it could work?