You dont really need an install tool to fit the balancer on an RB. Its ideal yes. But not a massive requirement.
You can just use the bolt to press it on as it has a large thread. But it can't be too tight a fit.
The reason they have have those install tools is for engines where the crank pulley bolt is only a 10 or 12mm bolt and will not be able to press the balancer on.
When i was looking at doing this, i looked at buying the tool to do it. They were all a generic tool with threads, adapters etc to fit a lot of engines. However none came with the M16/18? shank to suit the RB25 crank.
In the end, i just pressed it on with the crank pulley, it was actually a walk in the park. Pressed on very nice and easily. Put anti seize on the crank and wound the bolt in then torqued it. Easy.
The interference fit was very close to ROSS' specifications though.
I'm not sure how out yours is? You need a telescoping gauge and micrometer to creaturely measure the crank and the ID of the balancer.
EDIT - If its too tight you can't fit it period, this was done by a friend of mine with his ROSS balancer onto his engine, he didn't have a care in the world for specifications or the interference fit. Needless to say, when it was time to get the balancer off, it was almost impossible too and the crank had been damaged from such a tight interference fit.