[robespierre]

1. The system won't boot without graphics.

It should.

2. Have you ever replaced the real-time clock? That could be part of your problem (NIC needs to have proper MAC address to boot into miniroot)

Ding. The Indy has no serial ROM and stores its MAC address in the Timekeeper's battery-backed memory.

3. It sounds to me like a ram issue. The system uses 16 bit SIMMs and they are in banks of four. Do you have to remove an entire bank to test it. What sounds like happening is it's copying the mini root and unable to commit that over to the scuzzy drive. It could also obviously be a drive failure (did you properly partition it first?)

The Indy and Indigo2 use standard 72-pin parity FPM DRAMs, which are 36 bits per word. Each bank comprises four matching SIMMs, which must be 70 ns or faster.
A "Data Path error" concerns the memory controller, I think. But the OP said that the hardware tests passed, which is confusing.