Yes they are allowed, as you say without the airbox the standard rubber trumpets act as a rampipe so no problem with replacing these with spun alloy or even carbonfibre ones
Tyres are available by post from the same supplier that attends the meetings which is Protyre, give them a call and they will send some out to you
Dunlop Tyres Supply Via Protyre Motorsport
Tel: - 01782 411001
Fax: - 01782 411024
email:
sales@protyremotorsport.co.uk Dunlop D209 H-Rated Qualifier
120/70/17 Front
160/60/17 Rear