Mental help needed, please.

[Kalums]

Ok, I'm having straight forward decision making "funk" for lack of a better term. I need you all to help. Not so short back story: I've got a 1971 GMC K2500/flatbed, with a 350/ TH350/ NP205, Dana 70 dually rear-end, Dana 44 front 4.10 gears( Un-confirmed, that is what the "tag" on both axles says). I've already done a complete tune up(plugs, wires, cap, rotor, new HEI innerds, including weights and springs) rebuilt the Edelbrock 1406 that came with it and completely rebuilt the fuel system(tank, sending unit, fuel filter, fuel pump, fuel line to the carb) I've also replaced the starter and flex plate (both were missing teeth).I've also replaced mounts/lights/ and other aesthetic parts. .. At this point I'm getting frustrated... It will not time correctly or run smooth. I've tried finding TDC using a piston stop and it is way off(yes I rotated it by hand both directions and then found the middle) it will not stay "timed" I set it 12 dgrs advanced, shut of the truck, come back 10 mins later and it is "out" by 2 dgrs(either direction). There is also noticeable slop when turning the crank by hand to when the rotor actually starts turning. This to me tells me my chain/gears are toast and at some point I've developed a tick/tap in the driver's side of the engine that sound suspiciously like a lifter/valve/rocker or similar on #7.
**At this point I'm at a cross-roads.**
1) Do I continue to patch this possibly original ( I think the heads were replaced at some point) 53 year old engine "because it runs"?
OR
2) Swap in a Factory GM long block "TBI" 350 crate motor that has been sitting in the crate since 2017?

Any and all advice is welcome/appreciated.

[Getter-Done]

I would say swap it out.

You will be time and money ahead.

[Kalums]

Originally Posted by Getter-Done

I would say swap it out.

You will be time and money ahead.

This is actually the direction I'm leaning. I feel like I just need more experienced opinions than my own... Or put another way, "I value others (with more experience in this type of matter) opinions."

[wwboater]

Swap it and get it on the road to enjoy. If it is the original engine you will still have it and you can take your time tearing it down and really seeing what you have.

[Kalums]

Originally Posted by wwboater

Swap it and get it on the road to enjoy. If it is the original engine you will still have it and you can take your time tearing it down and really seeing what you have.

Valid point, thank you. I could tear it down and take my time rebuilding it the way I want for long term replacement... My wife is gonna laugh at me... I swore "no leftovers" ��

[geezer#99]

Tell us more about this tbi crate motor.
What’s the specs on it?

I’d keep plugging along.
You’ve got a running motor to learn stuff from.

[weq92f]

.

Crate motor.

-Kevin

[jabborabbo]

Originally Posted by wwboater

Swap it and get it on the road to enjoy. If it is the original engine you will still have it and you can take your time tearing it down and really seeing what you have.

This ^^^^^^^^^^^^^^