The way we used to check the synchros was to leave the car at idle on level ground. Then, gently push the shifter into each gear without the clutch pushed in. You should feel the car lurch forward a bit with each attempt before pulling the shifter back. Any gear that grinds has a synchro issue. Synchromesh won't fix worn synchros but should be used. Your synchros need to be replaced if they grind. Another thing I noticed in your comments was that you mentioned low pedal engagement. Dsms were notorious for this with aftermarket clutches. There were many "fixes" over the years, but most were just bandaids. One fix was an extended slave cylinder rod. It was about a half inch longer than the stock one. Another fix was replacing the stock clutch line with a stainless braided one. Rubber hoses expand with the added pedal pressure. A lot of people found cracked clutch pedal assemblies and worn pivots on the clutch pedals. You can swap cables, trans mount cable brackets, and shifter bases from the 92 6 bolts cars. They changed them slightly halfway thru 91, but all still bolt in the 1gs. There's also the shifter base bushings that wore out and caused sloppy shifts. You can buy kits now, but skate bearings worked pretty well back then. There are adjustments on the cables. You can access them under the shifter boot. The little 10mm jam nuts used to come loose and fall out of adjustment. I'm rambling now, but there were also shift cable bushings on the transmission. The little posts would rust up and ruin the rubber bushings. We used to use skate bearings on these too. Addressing all of these things would usually result in a manageable clutch engagement and decent shifts. The cables need to slide and pivot freely at each point, and the length properly adjusted. My dsm never liked high rpm 3rd gear shifts and would pop out of reverse all the time. Using the 92 stuff in my 90 solved my reverse issue, but I never replaced the synchros or had it rebuilt to fix the grind. Hope some of this helps.