Hi Samson,
I dont think you will have too many problems going up a tyre size, the original 3.25 front and 3.50 rear look very skinny compared to more modern bikes, Before anyone screams "what about originality???" your bike has long since been "racerised" so I think it will look sooo much better with a set of nice sticky looking tyres under it!
Measure the gap betwen the fork legs/mudguard stays, I am running a 90/90 x 19 front with no problems
I have a 100/90 x 19 rear again no clearance issues and I rekon theres enough room for a 110/90 rear
Avon roadriders seem to be popular and are getting good reviews, I have a few friends using them on gold stars and such and they are very happy!
Just my opinions again
Cheers
John O R