Originally Posted by ryansu

Welcome and congrats on the free score, a couple things to consider.

-gears is handy for determining how much rear sprocket your RD can handle
-if you have a bike co-op near you they are handy for vintage parts like say a long cage RD that can handle bigger cogs Shimano makes a 6 speed mega range FW with a 34t large cog.
-on most vintage double cranks 38t is about the smallest small ring you can go alternatively a compact crank (50/34) in a square taper BB version can be had inexpensively if you shop around.
-If your wheels are 27" there are two tires I really like; Panaracer Pasela 27 x 1 1/4 and on my touring bike I use the Sand Canyon (also Panaracer) 27 x 1 3/8 both are a bit more spendy then say a kenda tire but are plush and supple and, I think, worth the extra cost. I have ridden both on the type of hard packed trails you describe.

Have fun with your rebuild and enjoy riding the Soma, I am sure it will appreciate getting a second life.