If you're not fussed about engine angles etc, I don't think it'll be too hard at all for someone with good modelling skills.
Looking at the early Viper V10's I have, I don't think it's such a huge job. To me the easiest way is to use two engines if you can?
Cut one engine half behind the third row of cylinders from the front and the other engine half behind the second row of cylinders from the front. Now use three front cylinders from one and rear three (with transmission) from the other and match up the joins, remembering to keep the cylinder spacing the same. To me this would be the best place to do it as it cuts through the sump
pan, which could be cleaned up fairly easily or even covered with a thin
sheet of styrene to hide it. Obviously there will be some putty and sanding involved, but under the headers or the intake manifold, not much, if anything, can be seen when assembled. Just repeat for the other half of the engine.
Next, onto the valve covers, if they are like mine they have the Viper name and logos, so you may just have to shave these off completely first and then basically use the same above method as the block and heads, cut them three from the front and the other three from the rear (I think you can see where this is going). If you think that great big joint is too weak, cut the valve covers four from the front and four from the rear (using 4+2) and this would stagger the joints and give it all a bit of strength (a bit like brick work), plus help disguising the joint too.
The air intake manifold should be pretty simple using the same method as before. Now the exhaust manifold is a bit trickier. Depending on how much you think you will be able to see once assembled, you might have to fabricate small extensions of the exhaust runners, or cut one runner of the end of the spare manifold and add it to the V12 one. But you may just get away with a similar cut and shut as per the rest of the engine, depends on the header design.
Using this method might be slightly more complicated, but it only has one join to clean up, rather than two joins which are created by just cutting the engine and adding in a slice from another. Both methods involve using two engines, but a little thought and measuring before you cut will result in a neater job.
After all is said and done, it's up to you whether a 90 or 60 degree angle is that obvious to you, but I'm fairly sure not that many people will notice or even know about it.
Good luck mate, it's a bit of a job to do, but by no means impossible
and will look super cool 
Tim