There are hoods for them like this one
http://www.digikey.ca/product-detail/en/83-765/ARF1167-ND/160102
THe "N" connector is a standard panel mount unit.
The hoods aren't meant for "N" connectors,but for SO 239 connectors to attempt a match between their non-specified impedance & 50 (or maybe 75)Ohm cable.
"N" connectors
are 50 Ohm by design,so the hood may make things worse,rather than better.
The normal way of making fairly critical VHF/UHF connections to panel mount "Ns" is to cut the coax to have the shortest possible centre conductor & braid pigtail,& solder the latter to the round body of the connector as close to the centre pin as you can get.
500MHz sounds hellishly high in frequency,but,remember,a wavelength at that frequency is 600mm(roughly 2 feet in the King's measurements).
The pigtail lengths are miniscule in comparison.
That said,the "N" to SMA adaptor would look much nicer!