I need help converting Unity .shader to Shader Graph: Bumpy Glass

I’ve been tasked with converting an older Unity shader which does Bumpy Glass with some alpha modification, to URP. I’m assuming that means using Shader Graph. I’m a bit new to shaders in general, but managed to find various clues here and there and have come to the conclusion that creating a Custom Function is probably the easiest way (I could be wrong). Did I mention, this is targeted for WebGL?

Here is the original shader:

Shader "Custom/Glass-Seethrough Alpha" {
    _Color("Main Color", Color) = (1,1,1,1)
    _SpecColor("Specular Color", Color) = (0.5, 0.5, 0.5, 1)
    _Shininess("Shininess", Range(0.03, 1)) = 0.3
    _MainTex("Base (RGB)", 2D) = "white" {}
    _BumpMap("Normalmap", 2D) = "bump" {}
    _AlphaMap("Alphamap", 2D) = "black" {}
    _DistAmt("Distortion", range(0,256)) = 100
        GrabPass { }

        Tags { "Queue" = "Transparent" "IgnoreProjector" = "True" "RenderType" = "Opaque" }
        LOD 200

        #pragma target 3.0
        #pragma exclude_renderers gles
        #pragma vertex vert
        #pragma surface surf BlinnPhong alpha
        #include "UnityCG.cginc"

        float4 _Color;
        float _Shininess;
        sampler2D _MainTex;
        sampler2D _BumpMap;
        sampler2D _AlphaMap;
        sampler2D _GrabTexture;
        float _DistAmt;
        float4 _GrabTexture_TexelSize;

        struct Input {
            float2 uv_MainTex;
            float2 uv_BumpMap;
            float2 uv_AlphaMap;
            float4 proj : TEXCOORD;

        void vert(inout appdata_full v, out Input o) {
            UNITY_INITIALIZE_OUTPUT(Input, o);
            float4 oPos = UnityObjectToClipPos(v.vertex);
            #if UNITY_UV_STARTS_AT_TOP
                float scale = -1.0;
                float scale = 1.0;
            o.proj.xy = (float2(oPos.x, oPos.y * scale) + oPos.w) * 0.5;
            o.proj.zw = oPos.zw;

        void surf(Input IN, inout SurfaceOutput o) {
            half3 tint = tex2D(_MainTex, IN.uv_MainTex);
            half3 nor = UnpackNormal(tex2D(_BumpMap, IN.uv_BumpMap));
            half3 alpha = tex2D(_AlphaMap, IN.uv_AlphaMap);

            float2 offset = nor * _DistAmt * _GrabTexture_TexelSize.xy;
            IN.proj.xy = offset * IN.proj.z + IN.proj.xy;
            half4 col = tex2Dproj(_GrabTexture, UNITY_PROJ_COORD(IN.proj));
            half3 tinted = col * tint * _Color;

            o.Albedo = lerp(col, tinted, alpha);//tex.rgb * _Color.rgb * col.rgb;
            o.Normal = nor.rgb;
            o.Specular = _Shininess;
            o.Gloss = col.a;
            o.Alpha = alpha.r;
    FallBack "Diffuse"


The idea is to have the bump map animate on, say, uv.v, to simulate water flow through a pipe, and animate the alpha map to ‘reveal’ the pipe. Here’s what it should look like:
Supposed to look like

I found this article which helped (I THINK!) with the ‘vert’ part of the shader.
Where I’m getting stuck is in the ‘surf’ part. I’ve set up a bunch of inputs, and maybe I’ve gone down the wrong rabbit hole, but I’m getting an error saying that uv_MainTex does not exist:

Here’s a shot of the work in progress:
glass shader conversion WIP

And the full text (admittedly incomplete):

half3 tint = SAMPLE_TEXTURE2D(MainTex, SS, uv_MainTex);
half3 nor = UnpackNormal(tex2D(BumpMap, uv_BumpMap));
half3 alpha = tex2D(AlphaMap, uv_AlphaMap);

float2 offset = BumpMap * DistAmt; * GrabTexture_TexelSize.xy;
proj.xy = offset * proj.z + proj.xy;
half4 col = tex2Dproj(GrabTexture, proj);
half3 tinted = col * tint * color;

Albedo = lerp(col, tinted, alpha);

But I’m getting this error that uv_MainTex does not exist.
See error message

Am I even on the right track? Am I using the wrong macros? Do I need additional SamplerStates? Or hey, has someone already made such a shader I can get and call it a day?