Wanted: 3 speed freewheel block

picture's simply for illustrative purpose.

yes I got muddle up between the headset sizing and the chain sizing.

Was trying to build an 1950's british lightweight bicycle as lightly as possible, hence 3 speed transmission, by my calculation it should be a lots lighter than a hubs gear and 5+ speeds transmission and the frame I've acquired is stupidly light for it's time (double butted 531) designed for a rear derailleur only.

Really, a 3 speed 1/8" freewheel is going to be significantly lighter than a 5 speed 3/32"?
Get the scales out Ed, and give us numbers.