What was the first aircraft fitted with both an FDR & CVR?
It's not easy finding out which aircraft rolled-out with the first standard CVR/FDR combination. In fact it's so hard Google thought I was a robot, maybe I am.
Here's why, first this piece:

16 July 1964
COCKPIT voice recorders that will record all flight-deck conversations between the crew and ground control will be required in large passenger aircraft under new rules issued by the Federal Aviation Agency. Designed to assist in accident investigation and prevention, approved cockpit voice recorders will be required by July 1, 1966, in jets and turboprops weighing more than 12,500 lb. Pressurized four-engine piston aircraft will have to meet the requirement by January 1, 1967.
The installation of cockpit voice recorders supplements the existing requirement for critical-data flight recorders on similar aircraft. The latter, says the FAA, have been found indispensable in helping investigators determine probable accident causes, thus aiding development of ways to prevent accidents.

FDR's preceded CVR's and were already standard equipment on jets and turboprops weighing more than 12,500 lb. Then came the above CVR mandate to take effect by July 1966.
But, the CVR was not a new invention, and was already fitted to many aircraft, in fact, five months before the above piece we find this:

6 February 1964
Trans Canada Airlines has taken a world lead by announcing that it will spend \$1,360,000 to equip all its 78 aircraft with maintenance recording equipment. The airline has been investigating the use of the Royston Midas system for more than a year and last October took the decision to equip its fleet. Final details of the actual installations are now being decided, preparatory to placing a firm order, some additional steps having been taken as a result of the DC-8 accident at Montreal last November. TCA are to have a 93-channel system covering engines, movable surfaces, hydraulic and electrical systems and 15min of cockpit voice, installed in a safe location in the tail of its DC-8, DC-8F, Vanguard and Viscount aircraft. The installation will cost \$20,000 for each of the larger aircraft and \$15,000 for each Viscount and will be performed at Montreal and Winnipeg.
Next airline to place a major order for Midas may well be TWA, who have been conducting a systematic and successful investigation of its application for some time. The RAF first equipped one Britannia of Transport Command and has now ordered five recorder systems and four complete playback installations, presaging much more extensive adoption. British United Airways have also been flying a Midas-equipped Britannia for some six months.

Trans Canada Airlines being the first to equip a CVR/FDR/QAR combo well before the FAA mandate.
The CVR being an Australian invention, some sources say CVR's were required in Australia before the US, but given how many aircraft manufacturers were there in the mid-60's, it's near impossible to know which one was the first.
No one was eager to market their plane as the first that tells you why you crashed.
Most articles I found from the 60's were CVR manufacturers promoting their new products, but no aircraft manufacturer mentioning them. Example below:


Source used: Flightglobal Archive