Is this something the DLRA is likely to consider? I think they are specific to the LTA at the moment.
I've quoted the details from landracing.com below.
7.D.4.4 Production Twin (PT): (LTA ONLY)
Same as Production (P) for single and twin cylinder engines only. Pushrod and OHC engines with cylinder angles of 0 – 180 degrees allowed.
7.D.4.5 Production Twin Blown (PTB): (LTA ONLY)
Same as Production Twin (PT) with an original brand factory installed turbocharger or supercharger is required.
7.D.4.13 Twin Gas / Fuel (TG) and (TF):
Any 4-stroke motorcycle engine with 1 or 2 cylinders. Unlimited in design and modification. Pushrod and OHC engines with cylinder angles of 0 – 180 degrees allowed.
Subject to the same limitations as (G) and (F) respectively.
7.D.4.14 Twin Blown Gas / Blown Fuel (TBG) and (TBF):
Same as Section (TG) and (TF) above with a supercharger or turbocharger required. Subject to the same limitations as Classes (BG) and (BF) respectively.
7.D.4.6 Production Classic (PC): (LTA ONLY)
Same as Production (P) for 4-stroke air cooled engines manufactured between 1956 and 1986 inclusively.
7.D.4.15 Classic Gas / Fuel (CG) and (CF):
Any air cooled motorcycle engine manufactured between 1956 and 1986 inclusively. Extensive design and modification of engine allowed. Alteration of cooling fin design, size and placement is allowed. Any system designed to enhance cooling is not permitted. (This includes, but is not limited to water injection, nitrous oxide or water spray systems, radiators, enlarged oil capacity or modified oil systems.)
Fuel delivery may be modified or upgraded but OEM carbureted bikes must remain carbureted. OEM fuel injection may be retained, modified; or replaced by carburetors. No non-OEM engine management allowed. One distributor or magneto allowed. Computers are allowed for data collection purposes only.
7.D.4.16 Classic Blown Gas / Fuel (CBG) and (CBF):
Same as (CG) and (CF) above with a supercharger or turbocharger required.