I'm making this cake for a couple for their engagement party. I was just wondering if anyone has made something similar and if so, did you run into any problems with it? The engagement party is next weekend and I have so much on over the next few days that I dont really have time to do a practice run so any tips that you think might help would be greatly appreciated.
Also, I dont actually have a cake tin in the exact shape so I'm making 2 standard heart shaped cakes (2 layers per cake), making another square cake and cutting the 'tail' part of the heart out and attaching it before covering the cake in fondant. Do you think this will work? or does anyone have any suggestions?

Rather than adding the tail as a separate piece, it may work better to trim the hearts down.

You could also draw the hearts out on parchment paper or wax paper so that they match up like that, then cut each heart out and use it as a template to cut your cakes either out of a sheet cake or maybe even the heart pans that you have.
(Sometimes when I have a huge BCTF to make, I tape the sheets of wax paper together to get the width that I need. That would work here too if your cakes are bigger the normal width of a roll of wax paper.)