unfortunately there won't be much you can do about the compression issue, if the cylinders/piston rings are worn and/or valves not sealing good that would be quite a bit more work to fix. Resleeving and re-ringing pistons, headwork, etc.
A reman engine would be a better option versus all that work.
As for the fuel pressure, if the pump is bad it might could be rebuilt or just replace it with a reman one (or new depending if there is even a reman available).
The grid heater might gain some advantage helping it start easier but wouldn't work as well as a cold start kit (ether).
If there is a cold start option for it that might work better, ether always starts an engine quicker. There may be an aftermarket kit you can get for it if one isn't available from the mfg.
Just remember, with an old engine like that hitting it too hard with ether can be bad for it, but then again that goes for even a new engine. Ether lock up is hard on them and can break things if you're not careful.

The thing about the grid heater, if your environment is already somewhat normal (not cold) i'm not sure how much advantage you would get since the air going into the intake is already somewhat warm? The advantage may not be as good as you want.

I am wondering if adding the air intake grid heater would do the fix of depletion of fuel pressure and or compression. The motor is 22 years old and has over 7K hours so lack of sufficient fuel pressure and or compression could be from worn parts. It starts now with a shot of ether on the intake.

I was thinking the same thing about fuel pressure and or compression.

I am wondering if adding the air intake grid heater would do the fix of depletion of fuel pressure and or compression. The motor is 22 years old and has over 7K hours so lack of sufficient fuel pressure and or compression could be from worn parts. To repair that takes more time and money.

hmm, ok it seems odd it wouldn't have one but i guess if the climate is warm enough you shouldn't need one.
well...
bad injectors are one reason for hard or no start but you just replaced them...
what about compression, fuel pressure? have you checked those?

this motor has no glow plugs or any type of pre heater
there is a spacer where an optional air intake grid heater would go, but according to what I have read, I should not need one because I do not use the motor in a very cold climate.

what about the glow start?
should have one..
if the glow plug(s) are bad it will not want to start good

I originally changed all 4 injectors. But anyway, i followed your advice and bubble leak tested the injectors and found that 3 of them were leaking. So I removed the 3 and cleaned and lubricated the o rings and cleaned the internal bores the best I could and re installed them. No leaks now. Thanks for the tip on the bubble leak test.

My reason for changing the injectors is because I have been having to spray ether in the intake to get it to start for a few months now. The injector change out did not solve the problem.

Before changing the injectors i removed the fuel tank , cleaned it out, new hoses, installed a new lift pump and installed an electric lift pump from the fuel tank to the lift pump.

Besides the main fuel pump what else could it be?

yes it can, it goes into the combustion chamber so if a seal is bad it can leak like that if it does not seal, a compression leak. Besides if you didn't notice that leak before the injector replacement and now you hear it, that is sort of obvious (imo anyway). It wouldn't hurt to verify it.
An exhaust leak would be pretty obvious but being a diesel sometimes it is hard to pinpoint noises.

So it sounds like you're saying an injector leak can cause a tapping sound. Just wanted to verify that I will pull the suspect injector and install a new one

if you just changed an injector that would be the first place i'd look.
it may not have sealed correctly and is leaking around the seals.
check it by squirting some liquid around where it mounts and see if any compression is leaking around it being indicated by bubbles in the liquid.
the oring seals may be damaged during installation if your not careful when inserting it into the port.