"A cheaper alternative is a Trusty 6538."
Sounds like good advice to save a wad of $$.
I will say 65xx are cool today but I never ventured into a 6536/38 project because:
A passable 6536/38 should have a 'spring wire' plated brass bezel and correct size case. Many replica cases do not fit this recipe.
The 6536/38 is a little bit smaller than a 5512/13. Many of the replica 65xx are the same size as a 5512/5513 (maybe they used a 55xx case).
How do I know this ?
I owned a genuine 6538 for a few years before they were famous.
What do I think of them?
No offense but the 65xx (to me) looks like a 1016 that has been hit topside with a hammer, then a big crown and rotating bezel stuck on it. This is why I go for 5512 or 5513 projects...they look like a 'rolex', crown guards and all.
I feel I can diss the 6538 because I had one and this is the impression I've always had. Do not get me wrong, I would like to have a shoe box full of them now.
If anyone goes down the rabbit hole to put a Frankenstein 65xx together, be warned the cal 1030 movement is relatively fragile, expensive to buy, and expensive to maintain/repair.
How do I know this?
Experience, and I still have three watches with them...two 6605, one 6634.
The 6538 is famous because:
It is a classic vintage rolex.
The ficticious James Bond wore a 6538 in a few moviies.
Otoh James Bond also wore a Seiko.
Steve McQueen wore a 5512 and he was for real.
No Seikos that I know of.
He wore a Benrus 3061 in Bullitt, another cool watch imho.
A used Benrus 3061 will run from $25 to $125 on average (out in the wild, not on the 'net).
They are fairly cheap because they are not famous.