I think there is a question in there somewhere....
you are pretty much stuck with what ever your rim is so fatty, pizza cutter, whatever if your rim only takes a 130 rear then that is it.
what year 750?
Most cb750s can't go larger than 140 on a stock rim and even then the 140 has too much deflection because of the sidewall bowing out a little. the frame of most cb750s will also only go up to 150 (or 160 depending on the tire and model) before chain line becomes an issue. 77-78 bikes have a revised countershaft and the chain line can accomidate a 180 but the frame/swingarm wont usually (unless you hardtail it).
Sorry, i should have thought about what I was typing.
I heard that a 160 will fit my 74.
The best answer to that is "maybe". It depends on the rim and the tire.
no matter what a 160 will not fit a stock 1974 honda wire wheel. YOu might be able to shoe horn one on there but the sidewall will bow out and make the bike feel wobbly (and distort in turns). also you have to get rid of the chain guard and depending on the tire (whether it is a big 160 or a little 160) you still may have chain issues.
Chopper guys used to get 160s on the back by putting a 16" harley rim on the stock hub, this reduced the overall diameter and eliminated some of the sidewall rub issues but it is not the best for handeling because of the relativly large sidewall. Some of the sohc4 guys do a similar thing with cbr 600 f2 wheels that will give them a 160 on a 17" wheel but you have to watch for two clearance points: the inside upper vertical frame supports and the swingarm. F swingarms seem to take the wheel a little better or you can have one custom built to fit.
so your options for a wide tire are:
1) Lace a wider 18" diameter rim to your stock hub and use a 150 rear tire.
2) buy offset rear sprockets, lace a wider 18" rim to your hub and use a 160, get rid of any extranous brackets that rub and use a 77-78 F swingarm.
3) get either a cbr f2 rim or a 16" harly hoop
4)build a hardtail, use spaced out brackets, and put a 180 on the back, or
5) put a 130 on the back and forget about it
www.cyclexchange.net has a lot of wide tire stuff for a cb750, mostly for choppers. Take a look and see if it gives you any ideas.