The v8 is certainly not as wide as the dohc flat 6, but your right about height wise. The thing is though, the 914's 4banger was just a tad bit shorter then a v8 with a carb. Luckily the LS1 isnt as tall due to the efi and maf placement which would be flipped around. I need to locate some measurements for porsche 6, but I'm betting the LS1 can be fitted in there as I've found some LS1s that have been shoehorned to even tighter spaces ala 993s. As for the DME, isnt this just going to be replaced by the LS1 pcm anyway? Oh someone has already came up with the solution for mating an SBC (LT1 this time) to a boxster 5spd and resides in a 914 as we speak. Again my comfort tolerances are alot more different then others so aslong as that motor runs, the suspension works, and the drivers side window is down, I'm all for it
With a just a quickie google search, it looks like I can find non OBC cars and the DME looks like all it does is control the motor what nots. I think I can take the same approach as the FD Rx7 guys on how they deal with the ecm issue.