Crankshaft length and diameter are the critical issues so check the old engine and compare before ordering. Also, the Snapper muffler may not bolt up so you may need to fab something if clearance and exhaust direction are problems.The fuel system and wiring hookup should be straightforward.

Check the diameter and length of the Tecumseh crankshaft.

The $149 engine has a cast iron sleeve - a good feature. The 25MM crankshaft may be a challenge to adapt to the Snapper blade.

The $169 engine is an aluminum bore engine. This is the easy start engine with "Ready Start" according to the number - 123K02 0615. The actual engine will not have a primer.

Well heres another place to try where you might fined the exact model engine for your snapper

Here is a link that might be useful: small engine warehouse

I don't think either of the Harbor Freight engines will work. Those engines are for walk behind mowers, and will have light flywheels and zone-start control. Also, your mower should be similar to a 25066 which has four bolt mounting pattern (like larger engines) and requires 1" x 3 5/32 shaft.

New engines are no longer available as they don't meet emissions. You might find some old stock such as 6-8hp Tecumseh or 8-10.5hp Briggs, but not real likely.

Small Engine Warehouse does have a short block for $135, but you'll have to put all of your accessories on it. Trickiest part will be setting up the under-flywheel magneto and possible the governor linkage. Supposedly have one left.

Here is a link that might be useful: Tecumseh short block

When i need another used engine--i go out on the night before garbage pickup, and usually can find a used mower, maybe with a clogged carburetor, or some other minor flaw. I take them home, and next day i try to get them to run. You'd be surprised at how many good mowers are set out for pickup, all because of a simple thing like a dirty carburetor, or a bent blade! I make some good spending money thru these efforts, and if i can't fix them, then they get stored away for parts! If you mower is an older model, i think it would not be cost effective to install a new engine, but thats your choice!