I agree with Rossiz. I would keep the factory EFI...especially over a Holley conversion. I have built and Raced Holley carbs for many, many years, and I would never switch back to them over a factory EFI system. Conversion to twin Su's or Triple Webers/Mikuni's sure. But a Holley 4 bbl would be a step backwards IMHO.
The Holley is not going to like being perched above a stinking hot exhaust manifold... the Holley float bowls are even more sensitive to fuel peculation than the factory SU's. A really good heat shield and phenolic base isolator are a necessity.
The installation position of Holley's with that manifold is 90 degree's to their design position and this can cause float level issues under hard cornering. Mixture distribution to #1 and #6 carbs is less than ideal as well. This picture shows the improper " sideways" mounting and the lack of a heat shield. Bad design.
Holley aftermarket needle and seat are infamous for sticking open, causing massive flooding with raw fuel dripping out of the carburator. Use of Genuine Holley Needle and seats along with a good fuel pressure regulator will help alleviate the sticking N&S problem. However, the modular float bowl design of Holley 4150/4160 carbs always tend to have some full drip from the float bowls. Right on to the hot exhaust manifolds or header Not good.