Keep your six and build it up...that what my son did with his 65 Falcon and he's happy with the results. Its less common to see a well built Six, people notice.
Get a set of headers (next on our list), a dizzy, and a weber 2 bbl, your 90 hp motor will turn out 125-135 hp and still get gas mileage in the high 20's to low 30 mpg range with your stock rear end.
yeah, I know...it aint as cool as a V8, but you will spend more time behind the wheel for less money.
You probably have some kind of high rear end gearing like most old small fords, 2.83 or 3.08.
If you are not worried about long highway trips or gas mileage get a set of 3.55 or 3.73 gears and your little Falcon 6 will fly! I think My son's 65 Falcon 170 has 2.83 gears, a little slower off the line but cruisees nicely at 75 mph and gets somewhere near 26-27 mpg on 120 mile interstate highway trips.
Check out Classicinlines, and Cliffordperformance to see what I mean. I'm not making up this stuff, they have dyno results for many different inline six setups. you can see what each mod does because they have multiple dyno runs on the same car/motor with different dizzy/carb/headers/etc.
Parts are a little less common than sb stuff, but still out there.
I am planning on rebuilding the 250 in the Maverick I got today that threw a rod and split 2 pistons, if the block is rebuildable, if the block is shot, I'll swap to a 302 because it is easier to find one and is probably the easiest swap in the world.