Actually Clark I have quite a little stash of longer 303 bolt-heads. Unfortunately, not enough to start donating them.
That little paper-thin bolt body you refer to has survived military use in every continent of the World except Antarctica for 100 years. It has proved faithful in two World Wars, many more minor skirmishes and use in various bush-wars by so many nations and rag-taggle armies that they are uncountable. I even saw a 303 pictured in Sudan recently alongside the AKs. The 303 has killed masses of wildlife for sport and survival in every ex-colonial part of the World often with zero care. It has been successfully converted to handle the 7.62 NATO (308) cartridge. You really must step back and look at the reality of this, what appears to be to you, such a delicate firearm. You make a valid technical point but - a technical point has never been sharp enough to drop an enemy soldier.
My suggestion to RMKEY, subject to getting the required data, is to temporarily be prepared to exchange bolt heads between his three rifles. I am not making this suggestion now. I am saying, when we have the facts and have considered a couple of ideas, he may be able to put his favorite 303 into use by de-commissioning one of the other rifles by exchanging parts.
As information. In the past when I have re-barrelled a 303 I set the (what I would call) rim clearance to 10 thou. using custom made gauges. I have found this works with the majority of commercial brass. I do not use surplus ammo. I do not shoot 303 enough to justify using suspect, possibly corrosive, ammunition.