If you intend to put them inline, you should contact the guys at High Speed Salvage, if they still exist. They are the ones who did the V16 SBC years ago. They could actualy join two cranks and cams. You would still have two distributors and two oil pumps.
Engine bay clearence issues wouldn't be a problem. This would allow you to do a V12.
I have thought about this way more than I should.
Picture two OHC engines. Machine an aluminum section with a 90 degree top and boxed bottom. Mount the blocks on the 90 degree sections with main bolts and oil pan bolts. Put main caps on the bottom and align bore. Add a custom crank.
Mounting the heads would be the tricky part. With a fair amount of work, a guy could turn one head backwards and add a custom ground cam. It would require lots of custom machine work and parts.
Now if you wanted unique. Mount two sixes on a similar aluminum bottom section creating a V12. Leave the head arangement as it is. This would require two different custom intakes. One swept up and one swept down, so the carbs are level. Two cranks driving one common shaft mounted in the new bottom section. This could also be done with a U12 arangement. However, the dist in the middle would get hot. If a guy used two cranks he would need a way to sinc or time the engines together.
Now picture two Subaru engines stacked
Or two of those Mercruiser fourbangers opposed
When you spend a lot of time driving you spend too much time thinking about these things. The time isn't waisted if you think them thru to the point of solving some of the engineering difficulties. At least thats what I keep telling the voices in my head.
