Here is the formula for Champlin #16 (Edwal 36) which is probably the inspiration for FG-7.
Water 800 ml
Sodium sulfite, anhydrous 50.0 g
Chlorohydroquinone 25.0 g
Triethanolamiine, te4chnical grade 90% 11.0 ml
Water to make 1.0 l
pH 8.5 (FG-7 given as 8.6)
For use the concentrate is diluted 1+9 with a 10% solution of sodium sulfite.
It is important to use the technical grade and not the 98% purity as the technical grade contains some diethanolamine which provides the proper pH.
The MSDS for FG-7 indicates that it also contains hydroquinone. So you might try adjusting the formula to use both. You will have to experiment with the ratio of the two developing agents. I would suggest the equivalent of 10 g of hydroquinone and 15 g of chlorhydroquine to start. This corresponds roughly to the proportions in the MSDS. Of course you would not make up a whole liter to start until you get closer to a working developer that approximates FG-7. Increasing the hydroquinone will increase contrast while decreasing it will lessen it. Whatever you arrive at would be an FG-7 substitute and not actually FG-7. It is perfectly proper to do this. This actually could be fun to try. Let us know if you are successful.