Any Chevy V8 HEI from the early to mid 1980's is a drop-in fit. The distributor you have in the picture is not an original equipment item for a 265. It's one of the externally-adjustable distributors with a window in the side of the cap from the late 60's and early 70's, so somebody has already done an upgrade. The HEI you need will have two connectors in the cap and a vacuum advance unit. Stay away from the ones with no vacuum and a 4-wire connector coming from the distributor housing. Those require electronic timing advance from a computer. Run a 12 gauge or larger power wire all the way from the ignition switch to the HEI distributor.
Anytime a distributor is swapped, or even moved a little, the ignition timing is affected, so the timing will definitely have to be reset. It's also essential that the distributor gets installed properly to assure the right firing order is maintained. If you're having to ask these kinds of questions, you definitely need to find a pro to do the swap.
Jerry
