Another edit....sorry if this post is difficult to read...it is the result of multiple edits over an hour or two.
STOP...DONT ORDER THOSE SPOKES
Not if you plan to use the 'missing just 4 holes' idea.
OK< EDIT...NUMBER 23 ... Carry on, As you were soldier.
The difference between the spoke lengths, now calculated, are so small , for the non - radial "radial" pattern you are talking about , as to be inconsequential
but here they are of completeness
I have now worked out spoke lengths for you ..assuming the figures I have are these same as yours
Edit : is
this it
I found the ERD of the Rim 305mm,
That idea of 28 rim with 32 hub is going to give 4 different spoke angles so you will need 4 different spoke lengths. It wont be a true radial, as the angular spacing is just wrong.
I have done similar,
28 hole rim to 36 hole hub
The graphic below is for one side, you would 'rotate' the pattern 90 degree on the other side.
But if you are going to the hassle of buying new parts, I'd buy matching parts to start with..so a 32 and 32 or 28 and 28 . Tough if you have the rim and hub on order...continue....
See Chalo's post here
http://www.rideyourbike.com/36hub24rim.shtml
And these
http://sheldonbrown.com/rinard/36-24.htm
http://www.sheldonbrown.com/mismatch/
Also,
tips here in my post here, where I waffle on to myself (rather like this post) till I get to understand what this is all about, to get to grips with non decimal cross patterns / 'non whole number ' cross patterns
This post is mainly me taking to myself...but it helped me get my head around the concept and how to calculate the spoke angles from scratch
So back to your 28 hole rim, with 32 hole hub.
Spoke angles would be, as to be used in the calculations in the previous links:
0 deg
3.2 deg
6.4 deg
9.6 deg
Which is ( if Chalo can check)
0 cross
0.125 cross
0.25 cross
0.375 cross
So this gives :
136.56mm
135.59mm
136.69mm
136.86mm
View attachment 1