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Obtain a "Standard", off-the-shelf Single Phase Isolated Transformer, which has a 208V Primary, and 240V Secondary.
Feed the Transformer with a normal 208V 1 Phase 2 Wire + EGC (Equipment Grounding Conductor) Circuit.
On the Secondary side, ground either one of the "X" Terminal outputs... for example, Ground "X2".
Now you have a 240V 2 Wire system with an Ungrounded Conductor and a Grounded Conductor.
The correct way to describe your desired 240V Circuit is:
240V 1 Phase 2 Wire Grounded Circuit.
One "Side" of the Circuit is Ungrounded ("Hot" to Ground),
The other "Side" of the Circuit is Grounded - just like the "Neutral" on a 1 Phase 3 Wire Circuit, or the Common "Neutral" on a 208Y/120V 3 Phase 4 Wire Circuit.
Match the KVA rating to the KVA requirement for the test loads. Since the test loads are Resistance type loads, the power ratings will (almost always) be in KW (Kilo Watts).
If the Heaters consist of only Heater Elements, then the KW ratings will equal KVA.
If these loads only have Ampere ratings, multiply the Amperes by 240, which will show the KW / KVA rating.
Heater Element listed for 240V, FLA = 10
240 x 10 = 2400 VA (Volt-Amps)
Minimum KVA requirement: 2.4 KVA
Transformer size: 3.0 KVA