I advertise a few engines on Ebay, they are not built at this time but, I DO have all the parts to build it exactly THAT way at short notice if needed. When offering a few options, it is next to impossible to have every combination on the shelf.
I realize there are "not so trustworthy" sellers on there however, not EVERYONE should be painted with that wide brush.
For the most part, all my engines are built to customer spec. I advertise combinations that are more or less based on the type of parts (flat tappet, roller, cast, forged, etc.), and the final combination of cam specs, compression, displacement, will be based on the customer's needs.
There are times I will advertise a special engine, and that's usually based on parts I have in stock, but in every case, something gets changed based on the customer's application.
I've been down the road of building complete engines for sale, and don't plan to do it again. Every single customer wants something different. "Oh, that engine would be great, but....if only.....except", leaving the original engine in inventory, while I build something else for the customer.
I also require full payment up front (or in installments as we move from shortblock, to longblock, to complete engine). I'm not going to invest time and money in a custom build, only to have somebody come up short on the money when it's done.....lose their job, wife leaves them, get hit with a bunch of medical bills, whatever.
This is my business model, and it works for me. There's nothing unethical, or deceitful about it. My customers always get more
than they paid for.
In response to the OP....I've never heard of TNT, so I can't comment on their quality. I will comment that P-51 heads are the wrong choice for a street oriented pump gas stroker.