Dell has not released engineering info on whether your particular motherboard model 0R230R supports core2quad. What is leaked is that The Optiplex 760MT uses two motherboards - T674K Non-Quad core CPU motherboard U562N Quad core CPU motherboard

Actually you can not use 760SFF motherboard in DT case either. SFF board uses mini sata ATX 24 pin incompatible with standard ATX DT psu power connector.

Also for 760 SFF Only the SFF M863N specifically mentions support for a quad core CPU. There is no leaked data which 760 DT motherboard supports c2q. If you want to keep using the 760 DT case, the safest bet is to swap to SFF board M863N. MT board would not fit DT case. You also need to buy copper heatsink for optiplex DT to support 95W c2q. The added cost in the end may not justify. If I were you I would just get a complete optiplex 780 that supports c2q, instead of investing in miscellaneous parts to fix up old 760, but you may have a good reason to do so.

Also for 760 SFF “Only the SFF M863N specifically mentions support for a quad core CPU” However on eBay a seller claimed another SFF motherboard F373D also supports c2q. https://www.ebay.com/itm/Dell-F373D-Motherboard-w-Core-2-Quad-Q9400-2-66GHz-CPU-for-OptiPlex-760-SFF-/153435578297 There is no leaked data which 760 DT motherboard supports c2q. If you want to keep using the 760 DT case, the safest bet is to swap to SFF board M863N. MT board would not fit DT case. You also need to buy copper heatsink for optiplex DT to support 95W c2q. The added cost in the end may not justify. If I were you I would just get a complete optiplex 780 that supports c2q, instead of investing in miscellaneous parts to fix up old 760, but you may have a good reason to do so.

This is where i found that information https://www.dell.com/community/Optiplex-Desktops/Optiplex-760-DT-CPU-upgrade-fail/td-p/6032536 

if i need a coper heatsink for 95w cpu should 65w cpu do the trick?

but can i install 65w cdq