Hello funny farm, I have been in your predicament more times than I care to admit,(taking the 5th here!)....
So here is something you can do also.......
Take your route and save a copy to like TEMP_My Routes Name,,,,,,whatever, so can try this and not have to worry about any unforeseen errors, and trust me, you don't want problems with all the work you've done with your Route to this point.
Take the Temp Route file and add about 10 baseboards parallel anywhere on your route close to where you might merge this other Route you like, then just take a piece of Track and draw it out straight across those new baseboards. Make the first start of new Rail 25m, and the other end of it 365m, you probably need to add some splines in there? Then check then check the Grade of that Temp Track, to see what the % in rise it is....This is quick and doesn't take more than 10-15 mins I would think to see how steep the difference is between your route and the one your connecting, also, look at the new route, as to where it connects, to see if there is part you drop some elevation, and possibly raise a little bit on your Route, that may be all you need to make it work.....
I usually have to add blank tiles to some of my Merges that have height issues, there is no easier way with exception of what other folks said here, IPortals, and/or Helix will get the Job done, but still it takes time, I for one have never drawn a Helix, and I don't know that I could.
Also one other thought just came to me, you could run a heck of a long Tunnel into the side of the new Route and come up underground ground, but you'd still need those blank tiles to buffer the height difference of 25-365, probably make it look like the Rockies on one side, I don't know, but necessity is the mother of invention.
Edit:
Mr's Bleu came in and I lost the rest of my Train of Thought, (actually was time for dinner) never keep a lady waiting!
So what I wanted to say, we r just doing a quick and dirty setup to see what it might look like visually between the two routes and even if it doesn't work as intended at least you can see the level the track will look like when it transverses the difference in height. I had a merge route of difference of 1000' and thought I could lower the other one and redo the hill heights but it was too complicated and I had to disband the idea after seeing I could do it that way.
However with 300m I think you might be able to pull it off, another thing,with the Tiles, you could have a mountain ranges dividing your the 2 routes to have say the track going up 1/2 on one side and then curve around and climb the other 1/2 height, like a loop back?
I hope this makes sense, also you can make curves in the straight distance, which actually allows your Track a longer distance to climb the difference in height between routes.
I hope this may help you......