Lorin,
Why not try the pusher pump and see how you go before committing the £££ to reconditioning your IP? IP recons aint cheap by all accounts!
As Jon was pointing out, the IP performs 2 distinct functions: 1 is "sucking" the fuel from the tank to the IP and 2. is generating the very high pressures required to inject the fuel in vapour form quickly into the cylinders. The Walbro will obviously assist with function 1 but other than ensuring that ample fuel is present in the IP for function 2, the Walbro won't actually assist with the injection process.
Fitting the Walbro will give you a good idea whether insufficient fuel (i.e. function 1) was causing improper injection (function 2) if everything now works great.
Let us know how you get on!
Cheers,