The block on the 2.3 vauxhall was always suspect even with the thick wall thick web block used on the hs the center main could walk.
we use a special steel crank in the racer  the original vauxhall crank was designed for a v8 and when used in a four there is not enough counterbalance in the crank.We had a steel crank made with seperate counterweights per journal and that has cured the problem.valve weight and valve components limit the 2.3 single cam engine,we  had lightweight valves and titanium cam follwers with very expensive collars.the preent engine makes 234 bhp at 6900 revs on twin 48s.
The lotus engine uses a seperate cradle to support the crank and the crank itself is re wighted,the valve geqr is much lighter in the 4 valve engine.