Need help with HSF to fit my case

It largely depends on your motherboard and the position of the CPU socket.
With 750i boards the socket is very close to the standard PSU position so only an upwards blowing mount is possible with the XIGMATEK HDT-S1283.

The backwards blowing mount is better in general as the fan has more room to "breathe" and thus causes less noise.

If you mount a fan on the backside of the case you don't need push pull.
The case exhaust fan does that instead.

The air duct on the sidepanel will have to go BTW.
 
I see no need for that HSF unless you are going for a large overclock... You probably arent going to get a large overclock with a 750i... maybe a smaller HSF or stock cooler would work for you?

If however you do want to overclock opt for a better metal mounting HSF. The XIGMATEK with the added price of the metal mounting kit puts it in the same price range as the Thermalright Ultra 120 extreme. I would opt for the later and do some fine lapping to get the best mounting surface possible.