there are three main problems, assuming that you don't have the Victory book which covers it all in detail.
Belt drive, good question. The belts sold for conversions on 45s don't fit; you will need to fabricate a front pulley using the inner taper from a H-D unit and the outer ring from a British one. The belt will need sourcing - no British unit will be long enough - go to an industrial supplier with the original belt and total length for this question.
1) the primary chain sizes are different, as are the sprocket sizes. The 45 front sprocket is considerably larger than the British equivalent, as is the clutch. You will need to get an old sprocket, grind or mill the teeth off and fit a new tooth ring of the required size and alignment.
2) the alignment of the chain will need attention, assuming that you have the engine and rear wheel in the original offsets then this will be evident. This is done by offsetting the gearbox
3) the back wheel will need reversing as the rear drive chain will now be on the other side. There are various ways of doing this, all require some sort of welding to the brake anchor
reversing the wheel means that you will now need a revised rear brake linkage to suit. You also need a revised gear linkage. Opinions vary on this, but the two main alternatives are;
a) use the clutch pedal as a gear pedal. This means you need a linkage across the frame behind or under the engine. Use the original brake pedal as a brake pedal, which means you need a cross-over shaft like a panhead, or a cable linkage
b) use the original brake pedal as a gear lever. This isn't entirely satisfactory but it IS much simpler to do, it just needs a rod from the pedal and a cut-down gear pedal on the selector shaft as a crank. This means that you can fit a rod or cable to activate the ( now ) left side brake; a servicar clutch pedal is ideal for this.
you will now need a clutch lever and cable to fit your handlebars. Triumph 1" dia levers are ideal for this, H-D panhead style levers can be used but you will need to make a cable.
Shoot, a man could have a good weekend in Dallas with all that stuff...