I havent heard many BAD things about the Simmons system other than they fell out of fashion.
I think they were more expensive to build and sell. Others like Bendix had deeper pockets and could make a cheaper system so they got the lions share of the market.
The Simmons had the benefit of low Pilot workload. No fiddling with mixuture except to tune the cruise.
Nowadays, the biggest downside is the cost of repairing/maintaining such rare swiss watches.
I agree, a system which is easier and more cost effective to maintain would be nice; Even if it means I have to do more to manage the engine.
YIm guessing you need to (a) look for an STC on the subject. (b) find another application with the same engine core but the injection system you want, and use that design as Engineering Data for a Field approval for a 337 mod.