Firstly go and have a look, start thinking racer stop thinking bantam you don't need a road bantam to build a racer. The bantam bits you need can be bought for a few quid off ebay/Autojumble. Example frames £10-£30 I bought 2 for a £10 each, crank cases £15-20 max, internals a few quid, rear wheel hub £15, then if you doing a 175 you may need a crank to convert. Gear box is your stumbling point but there are CR boxes out there, expect to pay £150 or convert (lots of special engineering involved though)a road pair, our Ray and Steve Frayne run on them without any problem.
Buying, please read carefully 'Stay away from out of date piles of old crap off ebay' it would take you a lifetime to make em competitive, most of it will end up in the skip it will end in tears, best ask in the club and buy a proven racer.
Good luck to you all
Tony
ps how old is Zak and Tim?quite a few of us started at 16/17 and there's a few young uns giving the old brigade a run for their money
pps anyone want to update my build a 175 article? adding exhaust, carb setting, timing, chasis, bodywork etc