I'm not sure I would actually use 0-200s. I gather good ones are getting quite rare and overhaul costs climbing. Although the designer had a couple of ex Rallye 0-200s available I believe he envisaged using the 0-235 to power future airframes. But that was quite a while ago, and engines have moved on. For a homebuilt Speedtwin I would use a pair of the Jabiru 3300 six cylinder engines. 120 hp each side, nice sounding, smooth, economical, modern and substantially lighter than an 0-235. Reasonably affordable new, as well.
The original Speedtwin had a positive Sengine-out climb, even without featering props, and with two 0-200s that the designer himself described as pretty clapped out. So with a bit more power and lighter weight from the Jab engines, it should be OK to use lightweight wooden fixed pitch props, Chris Lodge or similar, and reap further benefits in low weight, smoothness and no worries about gyroscopic stresses when attempting those Zurakowski cartwheels!! However, propellors have also moved on and for people with deep pockets a pair of MT feathering VP props would probably be just the ticket.
Mmm, lovely daydream...