JD 7300 Planter - Narrowest Setting Possible

[powerstroker]

I have an John Deere 7300 vertical fold integral planter setup with eight MaxEmerge row units on 38" spacing. 

I want to narrow the planter spacings.  Does anyone know of the narrowest row I can get this thing to?  What's going to be my limiting factor?  The gearbox?  The wheels? 

Anybody got any tips for somebody changing the spacing?  Looks like once you loosen the U-bolts, it's jiggle & push til you get it where you want it. 

[mikeruss3019222]

Built one last year. Straight bar though. Put 18 units on 25' bar with 15 inch spacing and inside tractor tire spacing where we put the transmissions. Bolts holding pivot arms touch but it works very good.