302 heads wanted

Hi,
I`m new and my son has a 72 Dart were rebuilding together.We are building a 72 318 on a budget.We`ve been reading alot about using
302 (86-91)with 86-87 being the best years.His bottom end is stock
`72 318 in good shape.Cam is Mopar Performance purple .484 lift. We were told 1.88 and 1.6 valves at minimum to use.But I talked to a machine
shop in florida and they told me when we replace the valves with bigger it would drop cc. in chamber.They said to open them up to get back to range we want we would be defeating our purpose to gaine flow.What is best thing to do here.We read how easy the heads are to find for cheap but have had no luck locally.We saw some on craigs list but no one wants to ship them.E bay has some but there new with 1.78 valves.We would like bare heads or ones some one has reworked and moved on and wants to sell.Son has minimum wage job and hours are low due to going to high school.We need advise and help finding 302`s at a good price.He has loved Darts since he was a kid.PLEASE HELP IF YOU CAN.

Out of ideas Dad