I have developed a knock also and have simultaneously determined that my little SUV's engine ins not sufficient for 33" tires or towing. I have been researching swapping in a 6g75 for the last 2 days. I would like to swap information with you and what you have found. The block and heads are nearly identical to the 6g74 what has mainly changed is the bore, stroke, pistons, rods, wrist pin and intake runners. The 6g75is basically a stroker 6g74. Easy swap too. Just bolt on your accessories and sensor, plug it in and go. Same wiring harness and ECU. You can get your ECU reflashed to change the mapping and take advantage of the bigger bore and better flow.
Here are a few links that I have saved.

http://www2.pajeroclub.com.au/forum/showthread.php?t=40816

http://www.4x4wire.com/forums/showflat.php?Number=1255900&page=7

http://www.automotiveforums.com/t504521-discuss3_5l_montero_engine_swap__.html



http://www2.pajeroclub.com.au/forum/showthread.php?t=32790

http://www.rpw.com.au/shop/index.php?opt...t&Itemid=85

http://www.expeditionportal.com/forum/archive/index.php/t-100577.html

http://www.powertrainproducts.net/MITSUBISHI-6G75-03-07-3-8-V6-ENGINE-p/40.htm



https://www.rockauto.com/catalog/x,carcode,1417250,parttype,5240

http://club4g.org/board/eclipse-performance/33455-6g74-6g75-mivec-comparison.html