Tips and tricks for measuring slope of steam pipe?

After adding massive venting to my one-pipe, parallel flow steam residential system (three Barnes and Jones Big Mouths on the longer main and one Big Mouth plus a Gorton #1 on a much shorter main), I continue to have mild water hammer on a branch off my main. That branch off the main leaves my basement through a slight riser into a slightly smaller diameter main and then travels five feet to a riser to one radiator, another 15 feet to a 45-degree bend, then 10 feet to another radiator riser, then another 8 feet to another radiator riser, then 2 feet to another 45-degree bend, then 16 feet to a final radiator riser, then two feet to where it meets a drop-down dry return which runs vertically. That dry vertical return drops down as a dry return until it gets below the normal idle water line of the boiler, and then a wet return connects at a 45-degree fitting to run that wet return back to the boiler. My main pipes in the basement are all suspended on proper threaded rod and pipe hangers, and the slope measures out to approximately 1 inch drop per 20 feet of main, as closely as I can measure it (they are insulated, so it is difficult to take a precise measurement). But where the main branches out through a slight riser into that U-shape that I described in the crawlspace, due to nightmarish limitations on my movement in the crawlspace, it is all but impossible for me to accurately position a long level on the bottom of the main in the crawlspace to measure slope. Plus, some idiot decided it was OK to suspend that branch main through the crawlspace using steel straps, attached to the joists with nails in a very un-precise way.

I could probably measure down from the joists to the pipe top at various locations and then calculate the drop or lack thereof from those measurements off the joists, but I probably cannot get a long level in to measure along the bottom of that branch through the crawlspace. Using a level would be more accurate than measuring off the joists, since the 80-year-old joists are likely warped here and there. But space and access to the bottom of that branch through the crawlspace is limited by an air handler and ducts for a central air conditioning unit that takes up much of the crawlspace and limits my access to put a level along the bottom side of that branch main through the crawlspace.

I can't eyeball the pipe slope very well, either, since I added 2 inches of foil-faced fiberglass insulation to that branch through the crawlspace, to correct the insulation removal that some idiot did in a stupid attempt to warm up the floor of the bedroom above the crawlspace. The insulation I added is not precisely uniform, since it is spiral wrapped insulation, and not the beautiful plastic-encased snap-on insulation variety.

I have not yet flushed out the wet return line, since to do so properly I must detach an 80-year-old union that is near the beginning of the dry return and add a ball valve followed by a t-fitting, into which I can put a nipple that is NPT on one side and hose thread on the other side. I know that flushing that wet return will probably help the condensate flow back out of the crawlspace main more quickly and would likely reduce the water hammer in the crawlspace. But since my boiler water level returns to precisely the same level within a few minutes of boiler shut-off that it was at before the boiler fired, I feel that the flow through the wet return is at least average. If the condensate is flowing more slowly than it should through the crawlspace, I am guessing that the culprit slowing the condensate return is more likely to be erratic pipe slope rather than a semi-clogged wet return. I will eventually flush the wet return, but for now, I want to focus on checking the branch main slope through the crawlspace area, and correcting it as necessary.

Additional info: I installed a 0 to 3 psi gauge at the boiler, cleaned the pressuretrol pigtail and have the pressuretrol set to 0.5 and 1. Steam reaches the vents at both of the two main sections when the boiler 0-to-3 psi gauge is showing 2 ounces to 3 ounces of pressure, and the two sections of main get steam within 80 seconds of each other (with the section in the crawlspace getting steam 80 seconds AFTER the other section of main receives steam where it terminates). By the time the thermostat is satisfied and the boiler flame shuts off, my boiler pressure gauge shows about 31 ounces of pressure.

So, after all that lengthy description, does anybody have any tips and tricks to help me measure the slope of the main in the crawlspace, recognizing my limited access issues? I intend to install proper threaded-rod-held pipe hangers after I have adjusted the slope, as a replacement for the steel straps that are currently in place, and to adjust the slope if I identify any flat or sagging sections.

Thank you in advance for your advice and consultation.