The first leak you noted could just be the sender unit on the driver's side of the motor. A very common leak and if you want to try to fix it "on the cheap" just take the sender out, take it all apart. Reassemble, sealing it with silicone and reinstall. Or replace it, it isn't expensive.

If the rear main is leaking, but not badly, just live with it. It is possible it is leaking because the motor is overfilled or you have the wrong oil in it.

Same deal with the transxle, if it is overfilled or the wrong oil it will leak. Common sources of leaks are the output seals.

None of these items require engine removal. If you find you have to do the rear main it is easier to pull the transmission.

None of these items require a high skill level or a lot of special tools. I would suggest you do the oil sender first and then do an oil and filter change and clean up the motor and then watch for further leakage. Next drain and refill the transaxle with fresh oil and if necessary replace the output seals and flanges. If the exhaust manifolds aren't leaking there is nothing to do there.

If money is an issue then why are you considering a conversion to EFI? That can be very expensive. For a lot less money you can get the K-Jet going perfectly.

Before committing to replacing the motor a few basic checks are in order. Check the oil pressure, compression and leak-down rate. Measure oil consumption and determine if the head gaskets are good. If all of that checks out the only reason to replace the motor would be to get a few more HP or the block has rotted under the intake manifold.
One good way to clean up the engine bay is to spray the area with oven cleaner. Let it sit for a while and then hose it all off with plenty of water. Stay away from the top of the motor.