If you narrow the '81's K member this throws ALL of the suspension geometry out of whack... Handling will go out the window. Bump Steer, Ackerman, Roll Center Height, etc., etc. will all be effected badly. The vehicle won't drive right and you will have a hell of a time getting it lined up...
I would suggest forgetting the '81 full size and looking at an S10 front suspension instead. It will be much closer to the track width of your '53 and you should be able to install it without cutting it in half... Install the whole front frame section from the firewall forward.
There is a ton of aftermarket stuff available to lower the s10's also.