This is not a step by step write up as such but a guide showing how I did it, you will need to figure some parts out for yourself.
First you need to disassemble the blaster, it's not hard so I won't go any further in this step.
Now when you look at the pump there is two tubes, cut the one that leads into the tank and ONLY that one.
You do NOT need to plug it.
Now you need to cut out a strip in the tank. With the shell closed mark out the line so that when the shell is closed it cannot be seen.
Then cut it will a dremel, a nice high speed is needed to cut the thick plastic.
In the front section the hole needs to be wider so that you can squeeze the tank in.
Hot glue the tank in the following position.
Now this part is where your barrel will pass through, there's no room, we need to fix that.
Using the cutting bit remove some plastic so that there is room for your barrel to pass through.
Now you'll need to drill a hole through the front part so that your barrel can fit through.
Now you're going to need to cut the front nozzle off like in this picture.
Glue/Epoxy you coupler onto the nozzle, In used a 20mm UPVC coupler.
Now I forgot to take pictures of this part, sorry. You'll need to link the pin to your LSFG trigger with fishing wire, I used wipper snipper plastic blade because it was all I had and it's very strong. (It's the rope like stuff that cuts the grass)
When You've got them tied together you need to glue the LSFG handle in, I used super glue -> Hot glue -> Soon to add epoxy putty.
When you're done you'll have something like his.
Sorry about this write up being so vague but it's very hard to document in steps however if I can do it you probably can too.