I'm sure that the "Wrotham listening tests" carried out by the BBC in 1950ish would have been reported in Wireless World (The BBC reports are here
http://www.bbc.co.uk/rd/publications/rdreport_1950_30 and here
http://www.bbc.co.uk/rd/publications/rdreport_1954_36 )
To go up a few MHz would be do-able - probably all it would need would be to 'spread' the windings of the tune coils a bit. Going down to the low-tens of MHz would need new tuned-circuits in the front-end, and even then the variable-capacitor wouldn't have sufficient capacity-swing to cover many of the short-wave broadcast-bands without needing switched coils. An amateur-band receiver for, say, 14MHz, would be whaty I'd have done if converting this to SW. Remember that back in the 1950s most amateur voice contacts were made using classic AM.