You have an interesting project. Casting an aluminium block is relatively challenging and hopefully if i could share my experience casting aluminium blocks in Rhodesia 40 years ago, my learning mistakes might help you.
I cast an Aston DB4 replacement block on our farm. It was a process of trial and many errors but we eventually produced a couple of aluminium cylinder blocks that drove hundreds of thousands of km.
We made wood patterns easily enough but we found out the hard way that the casting pour must be achieved seamlessly with many pouring pots filled from three burners running flat out. We modified the water jacket and made the fire face an open deck which simplified the core making and placement. That required us to machine a huge cast iron monosleave containing all six bores. The cast iron monosleave overcame the constant overheating problems we had with the standard engine. An O ring groove was machined into both the top & bottom faces of the monosleave to seal water. We cross drilled the monosleave to improve water flow around the bores which helped cooling.
Sanctions against Rhodesia meant that we had to develop local fixes rather than simply importing vital parts from the UK. We only ever made aluminium castings and the following bullet points hopefully help your project.
1). Calculate and double check you have sufficient melting capacity. Theres nothing worse than completing 95% of a pour and running out.
2). We set up core boxes on a dry, flat, clean concrete floor (Mums carport). Important that the whole area is dry, ventilated and sheltered. Casting can be dangerous and our home made pouring laddles weighed a tonne. Modern health and safety professionals would never allow us to cast using the same methods today.
3). We did not try to make the machining allowances too small. Our castings were neither as accurate nor was well finished as factory castings from a proper founday. That necessitated
generous machining allowances.
4). We had significant leakage of moulton aluminium due to our amaturish moulds.
5). Runners and risers had a big impact on porosity and we no doubt made cylinder blocks that were not as well finished as factory made
6). Pouring needs to be swift but not hurried. I think we had about 8 people working on melting and decanting into our laddle and 2 of us pouring the part.
I cannot remember how many blocks we made in the learning phase but think we melted about 6 down before we made a workable sample.