That's assuming tax revenue remains the same, which
all economists agree will not be the case.
Whether or not Brexit will boost public finances is entirely down to how much of an impact it'll have on the UK economy. No one knows what the impact will be, but almost everyone agrees that it will be negative... though no one agrees to what extent.
So there's really two questions here: a) just how much more/less public money will be available? and, b) if there is more, how much of it will go to research?
No one knows the answers to either question, not even the government.
edit: a very quick back-of-envelope calculation based on the forecast tax receipts for 2014-2015 of 648.1bn[1]: 8.5bn makes up a whopping 1.31% of tax receipts. Unless I'm mistaken, tax receipts correlate strongly with the strength of the economy, so any more than a ~1.3% decline in the economy as a consequence of Brexit, would consume the "savings".
[1]: http://www.ifs.org.uk/bns/bn09.pdf