While I can't speak directly about the Remlin 783, I have done a bunch of projects with this clone's parent action the Marlin X7 (the action, trigger, bolt head, barrels, recoil lug and barrel nut are the same). Barrel change is not very difficult with the proper tools and headspace gage(s). The major PITA is timing the recoil lug. You don't have a "tit" on the recoil lug like a Savage. For lug alignment I now use a modified Wheeler #2 action wrench. I welded a recoil lug stop on the Wheeler, much easier now to torque the barrel nut. You can also make a jig from a piece of heavy wall PVC pipe that has a RCH bigger ID than the action OD. Dremel a stop slot for the lug on one end and drill a hole in the correct spot (good luck with that) to bolt the jig to the front action screw hole. Bolt is 1/4 - 32. You can get short 1/4 -32 bolts (older Harley gas tank bolts) on eBay or make your own with a die. Hard to explain in words but I can't get attachments to upload so I can't do pics. The PVC version works OK, but the modified Wheeler is much better.
I don't know of any replacement triggers. The Pro-fire style triggers, luckily, can be tweaked and with minor mods can be adjusted down to about 1.5 #, no creep, and nice crisp break. You just need to polish the sear and trigger engagement surfaces and swap out the trigger spring to a lighter spring. I use ball point pen springs. Also, over half of the trigger pull weight is the blade. If you treat it like a two stage, not too shabby. You can actually remove the blade (gasp) to further lighten trigger pull. I suspect that may stir up the safety lawyer Nazi dweebs, oh well. Not recommended for stumbling around in the woods while hunting. There is a U tube video on the pro fire trigger. It's for the XT-22 and XT-17. Can't seem to post links either, so you will have to Google "XT-22 & XT17 trigger job".
My index fingers are tired, I'm done. For further info, perhaps clarification, PM me.
Mike
Edit: The trigger pictured in the Utube video is the rimfire version, slightly different than centerfire, however the basics shown do apply. Only do the spring and polishing if required. Most of them, for hunting purposes, will adjust to 2.5# from the box creep free. Only 3 out of 15 so far that I have dealt with actually needed tweaking. If polishing is required (your trigger is creepier than Hilary), polish only, do not remove metal and change the geometry. These are MIM parts, surface hardened only. I use a dremel with buffing wheel and polishing compound. Only change the trigger spring if the pull weight can not be adjusted low enough for you. Both fixes are simple but a PITA. Lots of "jesus" clips. As in "JC where in the flock did that SOB go" Be careful.