[ngoma]

Welcome to D24T.com.

Starting these engines requires:

1. Good cranking speed-- strong battery/starter.
2. Good compression.
3. Good GPs, all 6.
4. Good fuel pressure, no air.

Are you sure the GPs are getting energized during your starting attempts? If the ether hits hot GPs then you got problems (cracked rings, etc.) but if the GPs are not getting juice then it might not turn out to be so catastrophic. But try to stop using the ether.

Trying to think of what might be causing the starting degradation. Did it slowly degrade or was it like all of a sudden? You said a month but that was not enough detail. Timing should not have changed by itself. GPs you can easily visually check for sound wiring, and check for sufficient voltage (11VDC) at the GP bussbar.

Low compression itself obviously can impair starting ability. Your "considerable blow-by and he burned a quart of oil every 500 miles or less" could indicate worn oil control rings, and possibly worn compression rings/cylinder wear. You could check compression after checking valve clearances, but I haven't seen where these engines need all that much valve adjustments.

Leaky IP shaft seal can cause difficult or impossible starting by allowing air to enter the IP. It won't always signal a failure by leaking fuel out, so the way to check is to splice a temporary clear fuel hose at the IP out (fuel return) to verify no air bubbles. Wouldn't hurt to verify no bubbles at the IP fuel in port, the fuel line at the IP in port should be (somewhat) clear.

Did the PO have records of timing belt replacement? If not, don't gamble; replace it. Interference engine! Requires specialty tools and knowledge.

Where were the orig. injector lines leaking? Monitor your "new" ones closely; they don't like (re-) bending or vibration (that's the reason for the clamps), and are subject to failure after trauma. The engine also doesn't like them to be different lengths.