tread wear is not going to be good with 11 1/2"s of tire on an 8 in wheel if my conversion of 295 width to 11 1/2 in. is correct. Looks good but wear suffers greatly, I have worn several sets out this way and they refuse to wear even as the sidewall wants to straighten at highway speeds which makes the center of the tire carry the load.
tire psi will have to be determined by how heavy the vehicle is. No real way to figure this other than the contact patch on the pavement. Run it through some water as stated to make sure all of the tread pattern is evenly hitting the road.