Folks might be a stupid question but I read you can't fit a 4.6 serp cover to a 3.9 or 4.2 block. I fitted one today and also the crank pulley. The obvious difference is the the cranks nose is shorter on the 3.9/4.2 and when you fit the crank pulley it is 20mm short of coming flush with the pulley. Is this the only difference. If a spacer was made and fitted would you then be able to use the serp cover. I rather it then the big bulky intrim serp cover.