Please help me decide on camshaft

[Nascar fan]

I have a 1994 Chevy Silverado P/U with 5.7L, 350 cu (L31) engine. I recently purchased new GMPP cast iron Vortec heads, an aluminum Vortec intake manifold, shorty headers, Holley 670 Street Avenger carb, and 1.52 roller rocker arms +timing chain, +HEI dist, racing wires etc., etc.

I am looking for more power and low end torque.

My intention was to install a used ZZ4 roller camshaft and roller lifters. But, after dissassembling the engine (still in vehicle) I found that I would have to drill and tap the three bolt holes intended for mounting the roller lifter retainer tray. I am concerned about getting metal filings in the engine cylinders and crankcase.

My second choice cam is a Howard Cams, CL112031, hydraulic flat tappet cam that I recently ordered from KMJ Enterprises. It is recommended for 4X4 and heavy vehicles.

My question is: Should I drill and tap the block and install the ZZ4 cam, roller lifters and pushrods, or should I just go ahead and install the new flat tappet Howard hydraulic cam, with new lifters?

Any comments on risk, horsepower and torque are welcome.

ZZ4 cam specs. -- .474/.510 lift, 208/221 @ .050, 112 separation (LSA)
CL112031 cam specs. -- .475/.475 lift, 232/232 @ .050, 108 separation

Note: While writting this note I came across another vendor with two additional Howard cams that make "good"/"strong" low to mid-range torque.

Can anyone provide advise? I am nearly at my limit financially, and the parts I've purchased will soon exceed the value of my truck.