If you have the bosses cast in the side of the bloack inline with the main caps then it is possible to house the 4.6 crank once teh mains are turned down however regards actually drilling holes for crossbolting it might not be possible as the interim 3.9 blocks didn't all have the required main caps for crossbolting.
Do you have the Des Hammill book? If so its covered in there but if not heres a quick low down on it.
Theres 3 types of 3.9 block.
The first is very similar to the 3.5 block just with bigger bores but the same early two bolt caps.
The middle one had the same main block casting as the 4.6 block so has the space inside to house the larger 4.6 crank (which the early one doesn't) and it had the bosses cast in the side for the cross bolts but it had the early 3.5 style caps which cant be drilled for crossbolting. If i remember correctly these have 14 holes drilled for head retention.
The last of them is identical to the middle block but it does have the caps which allow for crossbolting. These are almost identical (I think) to the 4.6 blocks other than the smaller main journal diameter and the lack of crossbolting. I believe these ones had 10 holes drilled for head retention each side.
If you have the later type don't ruah out with the black and dekker to drill for crossbolting just yet.
http://www.v-8.org.uk/FORUM/viewtopic.php?t=398
You could bugger your block up!
Some companies think its ok to do it and some don't. From all the info i've gathered about 1 in 5 will need line boring again.
I have one of each type lol, one of the early types in the car and the two later types in my garage. The middle one of the three types is a 36D engine no. I can't remember the rest although i'll take a look later.
Hope this helps!
Just checked, all three of my blocks numbers start 36D.
