Are you having to add coolant due to it disappearing, or dealing with any kind of engine overheating, external coolant leaks, or evidence of oil entering the cooling system?
Those would be the signs of headgasket failure. White smoke on a diesel engine, especially at cold start up, is much more likely to be a sign of incorrect engine timing or other combusion issue. But NOT a headgasket problem.
On a gas engine it is true that white smoke (steam) is the telltale for headgasket failure, but diesels more often show white smoke due to misadjustment. White smoke is the result of incomplete combusion of the fuel or combustion at the wrong temperature. Typically means the timing belt was last replaced by someone who did not have the correct equipment and/or did not understand the correct procedures or why they (and the tools) are necessary. It can also occur due to other reasons such as worn fuel injectors, a few dead glow plugs, or poor engine compression though I doubt that is likely in your case.
Contrary to what you may have heard, the original head gaskets are not "crappy" by any stretch. The can of course fail if the engine is overheated due to a burst hose, etc, or if incorrect timing settings and/or excessive modifications (too much boost/fuel) cause excess cylinder pressures far beyond design spec. But on vehicles that have had normal maintenance of the cooling system and are operated under reasonable conditions and expectations the head gaskets can last many hundreds of thousands of miles no issue. There is at least one known D24 that covered one million miles in hard taxicab use that never had the head off the whole time.
So ----- the good news is, it's much easier to correct the engine timing or replace a few glow plugs than replace a head gasket, and unless you are seeing cooling trouble the headgasket is almost certainly just fine and will STAY that way unless you burn up the motor or do something else to injure it.
It sounds like you have started down the path of doing some nice modifications. A bigger intercooler is always a good improvement for both power and engine health. And if you say it drives well and feels peppy, that is a good sign of a healthy engine too. BUT still, most of us here always like to recommend a good "STAGE 0" process before beginning any modifications. That means a full maintenance checkup of things like belts, hoses, cooling system, thermostat, radiator condition, all fluids, a check of the cold starting assist systems (glow plugs and timing advance system), and of course a full timing belt service, done correctly with all factory tools and procedures, unless you have rock solid evidence/paperwork documenting that this was done, correctly, within the last 7 years or 60k miles.
That Stage 0 process would likely identify anything causing this white fuel smoke on startup and give you a chance to resolve it.
Check out member ngoma's Hard Starting guide here to get some basics on glow system checkups. Since that is easiest you probably want to start there. Confirm all 6 glow plugs alive and well.
https://d24t.com/showthread.php?t=1225
Once that is done, move on to injection timing checks. Then if that is confirmed good, I would look at injector condition and do a compression test (at the same time -- makes sense to do with injectors out). If your engine is original to the 1984 car then it is old enough to have mechanically adjusted valves, thus you should check valve lash as well.
Let us know what you find!