That 40 series to 45 series is a difference but its not terrible..... 4.8 to 5.4 sidewall height. And the 305 over your 285 is only 11.22 to 12.01.

I would like to know what your rim width is.

I would think others have stuffed almost the same meat under it, but with a lift or a crank of the t-bar in the front. If it is what you want, do it, there is nothing you can't overcome.

My 20's are heavy chromes so I know where you are coming from...