Dunstall 810 front 18 rim

I have a Borrani 18 VM3 front rim (hub and forks are Dunstall stock).
I think , but not sure (i have never seen one before), that the stock rim was a 19 VM????.
On the rear there is a Borrani VM3 19.
Contraindications to use a front 18??
Ciao.
Piero

19 inch rear and 18 inch front rim is unusual on a Commando.
The other way roud (18 inch rear) is seen more often, because there is a wider selection of tires avalable in 18 inch.
Some say that a diversion from the 19 inch front and rear adversely effects the handling, but I can not speak from personal experience here.
Personally I would not choose for the 19' rear and 18' front setup.

I doubt anyone here has tried a 18" front/19" rear combination. Since you already have the rims, try it. At worst you are out the price of one tire. Big deal.