Lengthing the wheelbase, is it necessary??

[Bonechip67]

Stubbing a new/diff Nova subframe on my 53 shortbed 3100. The old sub was grafted level with the frame and measured out at 115.5 for a wheel base. I know its supose to be 116 but, if I lay the new sub under the stock frame do I have to lengthen the wheelbase? I have seen on here where guys have done so to make the wheels centered in the wheel openings, but I guess I dont understand while you would have to if you built it to the stock measurment of 116. Any insite would be greatly appreciated as im ready to weld mine up soon! Thanks in advance!