So ......are there any modern alternative engines for the Chippy ???
Can't imagine any, inline engines seem to be out of fashion and I'm sure there must be a reason. Perhaps the Wilksch diesel would fit? But that would likely be overweight.
For an unelegant solution to this problem on the SV4, find images of OO-KAT. But don't ask me how they ever managed to get approval for this mod, must have been one hell of paperwork.