Just to add two cents to the other suggestions...Egge Machine Co. at www.egge.com is another source for flathead parts. I'll also second the earlier opinion of starting with Reds Headers...very knowledgable guy and good to work with. Yet another source for some parts is eBay...lots of flathead parts up for auction - buyer beware of course - and be advised that most of the "bargains" have gone away as people tend to bid the price up (sometimes way past what they should) but you can still find some hard to find historic manifolds and carb cores for not bad money.

Flatheads forever - keep em running!