thanks for the advice pompompurin, actually the rep is superb YM 40 and well worth considering the upgrade.
Even if you decide to put a 2836-2 into your 2813 yachtmaster, the crown/stem/height on a 2813 / 2836-2 rolex rep is wrong compared to gen (one of the biggest rep rolex flaws). Then you will run into another problem of sourcing sub/yachtmaster hands that is compatible with the 2836-2 movement as you can't really buy good hands individually (maybe TDs can help you source them but it's difficult to buy nice hands on its own).
Once the cost start adding up for the 2836-2 movement upgrade with hands (£105 total?) AND assuming that the 2836-2 movement could actually fit inside your 2813 case (it might not fit because they are 2 different movements) AND you will likely need a new movement ring (£10 + time for trial and error for potential sanding to make the ring fit), then IMO it's not a time/cost effective project just to upgrade a cheapie 2813 when the watch is inherently flawed having the wrong crown/stem/tube height in the first place. Modern 6 digit Rolex reps with 2824-2 or the 3135/3130/3132 superclone movements generally should have the correct crown/stem/tube height like gen (with some exceptions, e.g. bp factory 16600 still has the wrong crown/stem/tube height even though it has a 2824-2 in it)
I recommend you have a look at the latest Noob Factory 116622 yachtmaster threads (this watch comes with 2824-2 movement or SA3135 rolex clone movement), it should blow your mind and 2813 away.. and the cost/time spent buying that and wearing it out-of-the-box is much more worthwhile than to upgrade a 2813 yachtmaster imo