What to tell the machine shop

one of the best things about building a slant is, unlike a V8, you really need to put parts together, you can’t just go catalogue shopping for a complete assembly.
My recommendations are:
1) get a really good handle on what you want concerning performance, octane level of the gas you want to use, how much you want to spend.
2) invest some time here at FABO and at slant six.org many folks have posted their slant six build combos.
3) know what you want before talking to a machine shop. Many shops are good, but you will get what they think you want, which may or may not be on target. The MS can be trusted to tell you how much the crank pins and journals need to be cut, how much the bores need to be opened to clean them up,,, but the target compression ratio, camshaft, what the cam gets degreed to when installed should be your call. Piston ring gaps should be what the piston manufacturer recommends.
If you spec out a motor and it does not do exacty what you want, you have still learned something. Let someone else make all the decisions and all you have is a motor.
4) one your basic questions like
Valves: Hughes Performance has drop in OS slant valves, although others have ran compatible Ford or Chevy valves, the F and C valves take a bit more set up as they have longer stems than the stock slant valve.
Pushrods are probably one of the last items to order, after the cam is installed and the head is done so you can measure to determine what length pushrod is needed and order the correct length.
So invest some time on a couple slant six forums, to get yourself familiar with the possibility’s and what is available in the aftermarket for slants, then figure out what you want.