Do NOT use silicone on the push rod seals. a) They work fine w/out the goop, b) you end up with a mess (as you've found) and 3) how will you ensure that a bit of silicone won't spooge out into the oil galley and subsequently block oil circulation.
There's no need for silicone goop (and make sure you keep the remains of the PO's mistake out of your engine).
As for removing carbon to improve mileage, I don't think you'll see much of a change. Much more inportant is what was your compression before disassembling? Healthy compression plus well tuned carbs will have the biggest impact in a stock motor.