The pinch blocks are absolutely a better way to go. As it is, I think you will might have luck swapping forks with a 500 or 550 with 35mm forks if it's even necessary, and depending on the spacing of the wheel. 750 might work just as well, but it seems it's never as easy to swap stuff as it may appear. Here is the link and a partial list of their 35mm trees :
http://www.caferacer.net/forum/project-builds/14059-triple-tree-fork-conversion-chart.htmlUpper: 26 x 48.5 x 15.2
Lower: 30 x 50 x 14.4
Honda C250N (79)
Honda CB250 (Early Models)
Honda CB250RS (80-84)
Honda CBX250RS
Honda CM250T Rebel (82-84)
Honda GB250F/F2
Honda MVX250 (83-84)
Honda VT250F (83-86), VTR250 (88)
Honda CB350F/F1 (73-74), CB350G (73), CB350/ K2-K4 (69-72)
Honda SL350 /K2/K3 (69-73)
Honda CB360 (74-76), CB360GT (76), CB360T (74-77)
Honda CJ360T (76-77), CL360 (74-75
Honda CB400A (74-75), CB400F (75-77), CB400TI/TII (78-79), CB400T (80-81)
Honda CBX400F
Honda CM400A/C/E/T (79-81)
Honda GB400
Honda CB450/K1-K7 (65-74), CB450T (82), CB450SC (82-86)
Honda CL450 /K2-K6 (68-74)
Honda CM450A/C/E (82-83)
Honda CB500/K1/K2 (71-73), CB500T (75-76)
Honda CX500 C/D (78-81)
Honda FT500 Ascot (82-83)
Honda GB500F/F2
Honda GL500/I (81-82)
Honda VT500 Ascot (83-84), VT500ED, VT500C/FT (83-84)
Honda CB550K/K1 (74-78), CB550F (75-77), CB550SC (83)
Honda CBX550F (82-83)
Honda CB650 (79-82), CB650C (80-81), CB650SC (82-85), CBX650ED/SCD
Honda CX650C (83), CX650ED
Honda GL650/I (83)
Honda VT700C (84-85)
Honda CB750K (69-78), CB750A (76-78), CB750F (75-78)
Honda VFR750C (83)
Honda VT750C (83)
Honda GL1000 (75-76)
Honda GL1000L (76)