This is an interesting thread.
I am running a sportscar that has had various engines fitted during its lifespan. From 6-inline BMW's to Mugen V8 F3000.
Now I have a 4-cyl. Volvo engine of an aged design (bought the complete car in Sweden - naturally it has a Volvo engine....). Its not suitable for a stressed application, so a solution had to be thought out for this car as well.
Remembering you stating apx. 20 mm. length to spare, you could do something similar to ease your installation.
Basically the car has a 10 mm. thick aluminium plate with holes fitting the tub. Given it is a sportscar, the tub is pretty wide - with your application the plate wouldn't be as big.
The plate is bolted to the tub using original pick up points, and bars to the gearbox are using the original pickup points too. The idea of this design is that it is very simple to add in additional engine mounts extruding from the plate and this way unstress the engine/making the engineblock more rigid.
Here you can see the plate and the left-hand engine mount.
Here you can see the right-hand engine mount and the adapter made to fit the gearbox - to create suitable pick up points. You'd probable not need that in your application.
Good luck with the build. Came to the site because of this tread and will follow it with great interest.
Regards,
Claus Møller
http://www.cm-motorsport.dk