Moelwyn & Port Madoc Railway
An early rail venture, predating the FR, but covering a similar idea was the Moelwyn & Port Madoc Railway (note the split name).
Although advocating a route up the Croesor valley, it would have carried some of the tonnage eventually carried by the FR Co.
In 1825, a bill was drafted and deposited at Westminster for the Moelwyn & Port Madoc Railway (MPMR).
It was promoted by Nathan Meyer Rothschild, who had interests in the area via The Royal Cambrian Company.
A bill was deposited in Parliament in 1825, an attempt at a similar connecting railway between Porthmadog and toward the Blaenau Ffestiniog area, using the Croesor valley, and surveyed by James Spooner.
The plan was for a "straight and flat"(ish) line of four miles from Porthmadog towards the mountains, followed by an incline and a four-way split, two of which reached over 2000ft up into the mountains. Whilst still "on the table", it was modified to extend to what is now Blaenau Ffestiniog.
The proposal was doomed to an early failure, in that it called for the expensive and time-consuming idea of hauling the output from Blaenau up 1200ft on one side of the Moelwyns, and then down 1900ft the other side.
In 1826, it was "lost" following objections, and the proposal died. There followed one of many depressions in the industry and the project folded.
There is a diagram in Boyd's history of the FR. 
Michael Lewis' articles covered this in more details