nice i looked at the small block chevey engine as to up the power its very cheap and a turn key engine was around £1500 to your door .

tbh with the price of the twin 40/45s , i would just put on a weber dgav 32/36 or the v6 weber 38 (bigger second choke port) and you can get a linkage so it opens both at the same time ( drink fuel mind you but revs really well) , i read that with this spec
good weber 32/36 carb
high lift cam
head skimmed
block skimmed
veriner pulley
light flywheel
4 branch
may need a geared starter due to compression
itg/kn air filter
gives you around 140ish bhp
so could be a idea as the extra cost of the twin 45s for around 15-20bhp?
hope this helps