Hi,
well the 5.500" rod you have are good for the 86mm crank.Of course it's quite triky when it's time to put the piston and cylinder with this combo (you will have to chek piston skirt clearanca at BDC).
I run this combo and works very fine!!.You will have more side load on the cylinder with those short rod comparing with the longer available today.And of course to go upper than 7500rpm longer would be better so as aked you ritchie,for what use is the engine?
ps:if you decide to go other rod please tell me