Ok then.  The 2014 Regs are on the Classic TT part of iomtt.com under competitors

In short the F2 class is 126cc - 350cc 2strokes in 2 groups.  1/1/68 to 31/1/86 and 1/1/87 to 31/12/92

4 strokes twins up to 750cc.  1/1/73 to 31/12/86
4 stroke fours up to 600cc.  1/1/73  to 31/12/86.

Road based race bikes fall into that category.  F2 was road derived engines fitted to race frames or road frames.  If it's a stroker you are considering I'd try and make it look race based.  Not sure whether an original LC would cut it.  350 YPVS look easy to TZify.

I'd contact the race office or you could end up like me last year.  Bike ready to go in F1 and got told just after the TT that I wasn't accepted.  In my case not a bike issue so I was told, just oversubscribed, and I wasn't quick enough in 2013 (22m59s) to make the cut.  However if it was an XR69 lookalike rather than a slabby 750 might I have made the cut ?  Much as you don't want to, I'd get it from the horse's mouth.