Creating a single graph with two different layouts (e.g. circle outside and unordered inside)

Question

I'm attempting to produce a graph using graphviz that produces a visualisation like this fantastic one(!; https://www.google.com/url?sa=i&source=images&cd=&ved=2ahUKEwjcgcDdvcHjAhXG854KHaMHB2EQjRx6BAgBEAU&url=https%3A%2F%2Fwww.kathartman.com%2Fvisualizing-detroits-civic-tech-ecosystem&psig=AOvVaw1P66IWi0HPrMZQMmEP_MuS&ust=1563642864370970). My current strategy is to produce an outer circle of nodes (achieved), and now want to add the nodes to the centre of the visualisation (unsuccessful thus far!).

I've explored subgraph clusters, which seems the cleanest solution, but haven't found a way to change the layout from the circo layout. I've also explored merging two different graphs but haven't discovered a way to do this as yet. I've also tried other r packages (E.g. visnetwork, networkd3, circlize) with diagrammeR/graphviz seeming the most obvious solution again...

grViz("graph {

      graph [bgcolor = 'white',layout = 'circo',
      outputorder = 'edgesfirst']

      subgraph cluster0 {
      node [shape = 'rectangle',fontsize = 22,fontname = 'Helvetica',
      fontcolor = 'black', width = 3, height = 1.25, style = 'dotted',
      penwidth = 5]
      '1'
      '2'
      '3'

      node [shape = 'plaintext',fontsize = 16,fontname = 'Helvetica',
      width = 1, height = 1]
      '18'
      '5'

      node [shape = 'plaintext',fontsize = 16, fontname = 'Helvetica',
      fontcolor = 'black']
      '4' 
      '9' 
      '6'

      node [fillcolor = OldLace,
      fontsize = 11,fontsize = 14]
      '7' 
      '8'
      '21'
      '22'
      '23'
      '10'
      '20' 


      edge [weight = 0.5,penwidth = 4, fontname = 'Helvetica',
      fontsize = '12', len = '1.5', color = 'gray80',
      arrowsize = '0.5']

      '1'--'18'
      '18'--'4'
      '4'--'7'
      '7'--'8'
      '8'--'2'
      '2'--'5'
      '5'--'9'
      '9'--'21'
      '21'--'22'
      '22'--'23'
      '23'--'3'
      '3'--'6'
      '6'--'10'
      '10'--'20'
      '20'--'1'}

      subgraph cluster1 {
      # Projects

      node [fontname = 'Helvetica',
      fontsize = '7', shape = 'circle',
      fixedsize = 'true', width = '0.5',
      style = 'filled', fillcolor = 'aliceblue',
      fontcolor = 'gray50']
      '11'
      '12'
      '13'
      '14'
      '15'
      '16'
      '17'
      '19'


      edge [weight = 0.25,fontname = 'Helvetica',
      fontsize = '12', len = '1.5', color = 'gray80',
      arrowsize = '0.5']

      '6'--{'10' '17' '19'} 
      '7'--{'11' '19'}
      '8'--{'12' '13' '14' '15'} 
      '9'--{'12' '13' '14' '16'}
      }

      }")

The goal is that the second subcluster (or 2nd graph) forms a network within the first subcluster, while still displaying the edges between. Currently, the 2nd subcluster populates the outside of the circle and remains in a circo layout