If setup on both bikes is different, then of course they will feel different. Get the road bike position sorted first, then you can adapt those measurements to the MTB, which is easy especially if it's a retro MTB and not a modern one (retro MTBs are a lot closer to road bikes than modern ones). You could get a professional fitting, but this will cost quite a bit and isn't really needed. I would start by using the "traditional" methods for determining saddle height, setback, and then bar position. This will give you a starting point, from where you can make small adjustments to feel the effects and find the position most comfortable for you.
And you do not need any particular length of crank. By all means try different ones, but don't think that for your height you must use a 165mm crank or whatever. Use what feels best.
And you do not need any particular length of crank. By all means try different ones, but don't think that for your height you must use a 165mm crank or whatever. Use what feels best.