Yeah... I'm with this remark...
"What kind of builder does not provide a cam profile ?"
If you're still fuel injected... knowing your valve timing is critical to tuning.
Despite this... lets' go with the the theory that the builder has a magical cam setup which cannot be broached to the tuners and owner.. They, in the least, should be able to suggest what your vacuum should be.
I've been in situations where I had a lot of overlap and the cam could not build vacuum for accessories. I went with a canister which provides a small reserve. Suffice to say that you'll never road race with this setup and if you're stuck in traffic, your brakes are more likely to feel manual than power.
There are expensive and heavy unit solutions where you can install an electrical vacuum pump. I say heavy because when I last looked it was a fairly stout looking accessory (moroso ?).
Another solution might be to consider a late model mustang brake system.. which finds it's power through the power steering pump, rather than relying upon vacuum. I had thought about this for my 1992 ...and I may return to the idea. Bigger fish to fry at this time.
Best Regards,
-D