To install a L52 in place of a L43 you must change...........
Fork, release bearing and collar, slave cylinder with push rod, two lower bellhousing bolts, trans handle, trim floor for top shifting handle instead of side shifter.
The crossmember, drivelines, starter, flywheel, pressure plate and clutch disk will all work just fine.
This was dead on - just finished a l43 to l52 and Marlin was dead on. no grinding needed on splines needed- the shifter rod is actually the same its just on the end there is a different size cap that will not work on the l52. the longer belhousing bolts was a hastle because the only ones i could find locally had a 19mm head vs stock 17 mm and you could not get a socket on it so i took the closest american and got it a little longer and threaded it in and put a lock washer and nut on and it worked perfectly. now running 75 down interstate and not wound up tight. everthing else was completely interchangable. Done