Bronze needs to be carefully fluxed when you cast it so Gary I'd keep an eye on that part- you're friend will tree up waxes to make those parts I'd imagine
unless he does sand casting as I do.. That's a good thing with 1/6 scale that the tracks are big enough that sand casting for especially the larger tracks becomes
even more viable than for 1/10 scale... If he uses your part as a master there will be some shrinkage difference between your original and the copies but it shouldn't amount to much, different metals having different shrink rates. I can't recall bronze but aluminum is about 1.5% or thereabouts. Aluminum should be strong enough for a hetzer link...

I'm very familiar with Geisβwerk, Martin Schroeder's work. I wrote about this a while back (Sad news).
I just received an email from his brother Stefan a few days ago. There still are some of Martin's original waxes left to be purchased if one has a casting firm to make the links for themselves. The loss of Martin and his marvelous work is one of the biggest hits to this hobby in years IMHO... people like Martin are so rare...
His work really helped 1/10 scale in particular; without it there aren't so many options- this helped push me into 1:6 scale and even there the loss is felt.

There's a fellow in the UK who is looking into having 1/6 King Tiger tracks cast in steel. It should make a beast of an Armortek model even more beastly. Definitely won't be run indoors!

Jerry