Stev-o, I don't have a problem, he asked, put in wrong number, I answered.
I don't think it's safe to use a too small 'width' tube except in an emergency, the tube will be stretched an so the rubber will be thinner.
In a tubeless tyre the friction can cause a problem (tubes can wear out because of friction with tyre casing as it flexes, tubeless tend to be 'rougher' internally than tubed)
I know 100mm is recommended as replacement for 3.25 tyre on CB750 but it is nearer 4.00 than 3.25 (25.4mm=1inch)
I haven't had a look at a CB750 for a few years but I'm pretty certain they have a WM2 rim which is only 1.85" where tyre beads sit
This may help

Your doing an expensive re-build, complain to the idiot who sold you wrong tube and get 3.50/4.00 tube
Put a dusting of talc in there when you fit tyre to rim, it helps things slide around